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Question 6753: Omitting One Existing Factor and Multiplying Back

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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R0012-06753 · q-20261010-advance-20261014-r05-factorial-0078

Original question and givens

N begins at 0, F(0)=0!=1, and factorials use exact integer arithmetic, not floating point. n=4, k=3∈[1,n]. Give (n!, product with k omitted once n!/k, k times that product minus n!).

  • G001 — N begins at 0, F(0)=0!=1, and factorials use exact integer arithmetic, not floating point. n=4, k=3∈[1,n]. Give (n!, product with k omitted once n!/k, k times that product minus n!).

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

N includes0;F(0)=1;F(j)=j·F(j−1)

After

exact integer products,not floating values or a permutation proof

Conditions: none

Use empty product1 and integer factor multiplication,retaining large values exactly.This finite recurrence audit is not a general proof of permutation counting.

Step identifiers and dependencies

Rule: exact_factorial_protocol · Uses: G001

S002 · implies

Before

actual factorial:start at F(0)

After

F(0)=1

Conditions: none

The product of zero factors is1,not0;this is the successor recurrence's base.

Step identifiers and dependencies

Rule: factorial_empty_product_base · Uses: G001, S001

S003 · calculation

Before

actual factorial through factor1 := mul(1, 1)

After

actual factorial through factor1 = 1

Conditions: none

Multiply the preceding factorial by the new positive integer factor,retaining every exact intermediate.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

actual factorial through factor2 := mul(1, 2)

After

actual factorial through factor2 = 2

Conditions: none

Multiply the preceding factorial by the new positive integer factor,retaining every exact intermediate.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · calculation

Before

actual factorial through factor3 := mul(2, 3)

After

actual factorial through factor3 = 6

Conditions: none

Multiply the preceding factorial by the new positive integer factor,retaining every exact intermediate.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · calculation

Before

actual factorial through factor4 := mul(6, 4)

After

actual factorial through factor4 = 24

Conditions: none

Multiply the preceding factorial by the new positive integer factor,retaining every exact intermediate.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

single-factor-omitted product := div(24, 3)

After

single-factor-omitted product = 8

Conditions: none

The nonzero k occurs exactly once in the1,...,n factor list;removing that factor gives n!/k.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · calculation

Before

restore omitted factor := mul(3, 8)

After

restore omitted factor = 24

Conditions: none

Multiply the same k back to audit the complete product.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · calculation

Before

restored product minus factorial := sub(24, 24)

After

restored product minus factorial = 0

Conditions: none

Restored product minus the true factorial must be0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · implies

Before

removed factor k=3;full n!=24

After

omitted product=8;restoration residual=0

Conditions: none

Omit the designated factor once,not every factor divisible by k;check by exact positive-integer division and reverse multiplication.

Step identifiers and dependencies

Rule: single_factor_removal_reverse_audit · Uses: G001, S009

Reverse checks

  • S010 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S009 · premise_and_result_audit — Recompute restored product minus factorial with exact rational arithmetic, not rounded decimals.
  • S008 · premise_and_result_audit — Recompute restore omitted factor with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Recompute single-factor-omitted product with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute actual factorial through factor4 with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Recompute actual factorial through factor3 with exact rational arithmetic, not rounded decimals.
  • S004 · premise_and_result_audit — Recompute actual factorial through factor2 with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute actual factorial through factor1 with exact rational arithmetic, not rounded decimals.
  • 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

(24, 8, 0)

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: 7d2827405f2f6068c178d6329b0d115eb7cd48005836c0434b7ed438592d150f
  • candidate record SHA-256: 77c65c80e3bdd6c2bf6019edf62fe946c1d82cf757f21f9eb4d73f7d28cdf236
  • semantic review receipt SHA-256: 90dbc494b2d34ef51f412dcff63cfcc1a2215d038bff71f38f5dded4c64faf00
  • question-first witness SHA-256: b72a3b8bcf10f584396e0dd5198c657b0934a71864e5a3fa6321d7a613aef9f9
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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