A326039 Largest square dividing the sum of divisors of n: a(n) = A008833(sigma(n)).

1, 1, 4, 1, 1, 4, 4, 1, 1, 9, 4, 4, 1, 4, 4, 1, 9, 1, 4, 1, 16, 36, 4, 4, 1, 1, 4, 4, 1, 36, 16, 9, 16, 9, 16, 1, 1, 4, 4, 9, 1, 16, 4, 4, 1, 36, 16, 4, 1, 1, 36, 49, 9, 4, 36, 4, 16, 9, 4, 4, 1, 16, 4, 1, 4, 144, 4, 9, 16, 144, 36, 1, 1, 1, 4, 4, 16, 4, 16, 1, 121, 9, 4, 16, 36, 4, 4, 36, 9, 9, 16, 4, 64, 144, 4, 36

Offset: 1

Author

Antti Karttunen, Jun 05 2019

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A008833, A326038, A326040.

Programs

Mathematica

Module[{sqs=Range[100,1,-1]^2},Table[SelectFirst[sqs,Divisible[ DivisorSigma[ 1,n],#]&],{n,100}]] (* Harvey P. Dale, Jul 29 2019 *)

PARI

A008833(n) = (n/core(n));
A326039(n) = A008833(sigma(n));

Formula

a(n) = A008833(A000203(n)) = A326038(n)^2.

a(n) = A000203(n) - A326040(n).