Question 22120: The Forward Transform Sums over All Positive Divisors

Original question and givens

Use positive integer n=20, exact integer arithmetic function f(k)=a*k+b with a=5, b=7. F(m) sums f(d) over every positive divisor d of m. Inversion uses mu(d)*F(m/d); complete prime multiplicities determine mu, with mu(1)=1. Do not replace d|m by d≤m or use only prime/proper divisors. Give (n, divisor_value_rows, F_n, certificate).

• G001 — Use positive integer n=20, exact integer arithmetic function f(k)=a*k+b with a=5, b=7. F(m) sums f(d) over every positive divisor d of m. Inversion uses mu(d)*F(m/d); complete prime multiplicities determine mu, with mu(1)=1. Do not replace d|m by d≤m or use only prime/proper divisors. Give (n, divisor_value_rows, F_n, 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.

• mko-mobius-inversion-finite-divisors

Step-by-step derivation

source operation=mobinv-forward-divisor-transform;original snapshot and mathematics retained

explicit ordered source output fields=[n, divisor_value_rows, F_n, certificate]

Mobius inversion ORIGINAL forward:actual positive input=20;check complete integer range1..20

ALL positive divisors INCREASING=[1, 2, 4, 5, 10, 20];not only primes/proper divisors or all integers<=n

Mobius inversion ORIGINAL forward f(1) ORIGINAL a times divisor := mul(5, 1)

Mobius inversion ORIGINAL forward f(1) ORIGINAL a times divisor = 5

Mobius inversion ORIGINAL forward f(1) plus ORIGINAL b := sum(5, 7)

Mobius inversion ORIGINAL forward f(1) plus ORIGINAL b = 12

Mobius inversion ORIGINAL forward f(2) ORIGINAL a times divisor := mul(5, 2)

Mobius inversion ORIGINAL forward f(2) ORIGINAL a times divisor = 10

Mobius inversion ORIGINAL forward f(2) plus ORIGINAL b := sum(10, 7)

Mobius inversion ORIGINAL forward f(2) plus ORIGINAL b = 17

Mobius inversion ORIGINAL forward f(4) ORIGINAL a times divisor := mul(5, 4)

Mobius inversion ORIGINAL forward f(4) ORIGINAL a times divisor = 20

Mobius inversion ORIGINAL forward f(4) plus ORIGINAL b := sum(20, 7)

Mobius inversion ORIGINAL forward f(4) plus ORIGINAL b = 27

Mobius inversion ORIGINAL forward f(5) ORIGINAL a times divisor := mul(5, 5)

Mobius inversion ORIGINAL forward f(5) ORIGINAL a times divisor = 25

Mobius inversion ORIGINAL forward f(5) plus ORIGINAL b := sum(25, 7)

Mobius inversion ORIGINAL forward f(5) plus ORIGINAL b = 32

Mobius inversion ORIGINAL forward f(10) ORIGINAL a times divisor := mul(5, 10)

Mobius inversion ORIGINAL forward f(10) ORIGINAL a times divisor = 50

Mobius inversion ORIGINAL forward f(10) plus ORIGINAL b := sum(50, 7)

Mobius inversion ORIGINAL forward f(10) plus ORIGINAL b = 57

Mobius inversion ORIGINAL forward f(20) ORIGINAL a times divisor := mul(5, 20)

Mobius inversion ORIGINAL forward f(20) ORIGINAL a times divisor = 100

Mobius inversion ORIGINAL forward f(20) plus ORIGINAL b := sum(100, 7)

Mobius inversion ORIGINAL forward f(20) plus ORIGINAL b = 107

Mobius inversion ORIGINAL forward full forward divisor sum := sum(12, 17, 27, 32, 57, 107)

Mobius inversion ORIGINAL forward full forward divisor sum = 252

Reverse checks

• S015 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward full forward divisor sum with exact rational arithmetic, not rounded decimals.
• S014 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(20) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(20) ORIGINAL a times divisor with exact rational arithmetic, not rounded decimals.
• S012 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(10) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S011 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(10) ORIGINAL a times divisor with exact rational arithmetic, not rounded decimals.
• S010 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(5) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S009 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(5) ORIGINAL a times divisor with exact rational arithmetic, not rounded decimals.
• S008 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(4) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S007 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(4) ORIGINAL a times divisor with exact rational arithmetic, not rounded decimals.
• S006 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(2) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S005 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(2) ORIGINAL a times divisor with exact rational arithmetic, not rounded decimals.
• S004 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(1) plus ORIGINAL b with exact rational arithmetic, not rounded decimals.
• S003 · premise_and_result_audit — Recompute Mobius inversion ORIGINAL forward f(1) ORIGINAL a times divisor 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

(20, [[1, 12], [2, 17], [4, 27], [5, 32], [10, 57], [20, 107]], 252, sum_over_all_positive_divisors)

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.