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Question 22751: The Recurrence and Both Closed Forms Use the Same Zero-Based Index

On this page
  1. Original question and givens
  2. Definition and scope
  3. Step-by-step derivation
  4. Reverse checks
  5. Result
  6. This question review and source binding

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R0044-22751 · q-20261014-advance-20261111-r05-catalan-numbers-0051

Original question and givens

Use natural index n=0≥0, C_0=1 and C_(n+1)=sum over i=0..n of C_i*C_(n−i). Exact BigInt coefficients and answers are retained. Do not shift to a C_1-based convention or truncate a nonintegral quotient. Give (n, recurrence_value, closed_value, difference_value, all_equal, certificate).

  • G001 — Use natural index n=0≥0, C_0=1 and C_(n+1)=sum over i=0..n of C_i*C_(n−i). Exact BigInt coefficients and answers are retained. Do not shift to a C_1-based convention or truncate a nonintegral quotient. Give (n, recurrence_value, closed_value, difference_value, all_equal, certificate).

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

Step-by-step derivation

S001 · implies

Before

source operation=catalan-recurrence-closed-cross-check;original snapshot and mathematics retained

After

explicit ordered source output fields=[n, recurrence_value, closed_value, difference_value, all_equal, certificate]

Conditions: none

Keep the historical interface marker and list ordered source fields without JavaScript.Tags are not additional evidence;fixed No markers retain their scope.The ordering helper supplies protocol order,not mathematical correctness.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL requested natural index n=0

After

initialize C_0=1;recurrence C_(j+1)=sum_i=0..j C_i*C_(j-i),including ALL splits

Conditions: none

There is one empty object,so C0=1.Include every split i0..j for C_(j+1),without a C1-based index shift.

Step identifiers and dependencies

Rule: catalan_base_case_empty_object_C0_one · Uses: G001, S001

S003 · implies

Before

Catalan central:ORIGINAL binomial N=0,K=0

After

use k=min(K,N-K)=0;initialize exact product1;empty product for k0 is1

Conditions: none

Use binomial symmetry to shorten the product while retaining original N/K roles.Multiply before each exact division,without floating-point factorial approximations.

Step identifiers and dependencies

Rule: catalan_exact_binomial_product_initial_and_symmetry · Uses: G001, S002

S004 · calculation

Before

Catalan ORIGINAL denominator n plus1 := sum(0, 1)

After

Catalan ORIGINAL denominator n plus1 = 1

Conditions: none

Substitute original roles,indices and established intermediates exactly,not floating-point approximations or another question's data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · implies

Before

ORIGINAL n=0;central binomial=1;positive denominator n+1=1

After

Euclidean quotient=1,remainder=0;check remainder0 BEFORE treating quotient as Catalan integer

Conditions: none

Check remainder0 before taking an exact integer quotient.Do not hide nondivisibility by truncation;retain denominator1 and central1 at n0.

Step identifiers and dependencies

Rule: catalan_remainder_BEFORE_exact_closed_division · Uses: G001, S004

S006 · calculation

Before

Catalan exact closed quotient after remainder0 := div(1, 1)

After

Catalan exact closed quotient after remainder0 = 1

Conditions: none

Substitute original roles,indices and established intermediates exactly,not floating-point approximations or another question's data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · implies

Before

Catalan adjacent:N=0,K=1

After

K outside0..N,so binomial=0

Conditions: none

The source convention gives0 outside0..N,including choose(0,1) when n0.

Step identifiers and dependencies

Rule: catalan_binomial_out_of_range_zero · Uses: G001, S006

S008 · calculation

Before

Catalan central minus adjacent binomial := sub(1, 0)

After

Catalan central minus adjacent binomial = 1

Conditions: none

Substitute original roles,indices and established intermediates exactly,not floating-point approximations or another question's data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · implies

Before

ORIGINAL n=0;recurrence value=1;central=1,adjacent=0,denominator=1

After

closed quotient=1;binomial difference=1;ALL THREE agree;balanced paths counted by choose(2n,n),bad paths first-crossing reflection counted by choose(2n,n+1)

Conditions: none

Reflect a bad balanced path through its first crossing of−1 to obtain a path with n+1 ups and n−1 downs,so good paths are the binomial difference.First-return decomposition U P D Q gives the Catalan convolution with empty-path base1,uniquely determining the same count.The adjacent-binomial ratio yields central/(n+1).This is a general argument,not extrapolation from finitely many equalities.

Step identifiers and dependencies

Rule: catalan_general_Dyck_reflection_and_first_return_recurrence · Uses: G001, S008

Reverse checks

  • S009 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S008 · premise_and_result_audit — Recompute Catalan central minus adjacent binomial with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S006 · premise_and_result_audit — Recompute Catalan exact closed quotient after remainder0 with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S004 · premise_and_result_audit — Recompute Catalan ORIGINAL denominator n plus1 with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S002 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(0, 1, 1, 1, Yes, C_zero_index_convention_preserved)

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.

Source hashes and review receipts
  • input commit: 0f7be61e2c22317a4075561dc822c87d881a50db
  • original question SHA-256: 6de38e28f1fb49bca03ab5c715bc23fcb295f7afae1c2878431c5b139d11caa4
  • candidate record SHA-256: 1c48eecc3b441be194d79a01e146b1085d0aacb90a39db26043d01aa396dbd23
  • semantic review receipt SHA-256: 89b8e810eced1a69dbfef28d4b112e829edf156c7905a86e39a3f4958cd75e81
  • question-first witness SHA-256: b2e8b769c463242f05172564ae96e310403eae151e1ec30bcb50be3ffe12cfc7
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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