A378994 a(n) = gcd(2*n, sigma(2*n)).

1, 1, 6, 1, 2, 4, 2, 1, 3, 2, 2, 12, 2, 28, 6, 1, 2, 1, 2, 10, 6, 4, 2, 4, 1, 2, 6, 8, 2, 12, 2, 1, 6, 2, 2, 3, 2, 4, 6, 2, 2, 28, 2, 4, 18, 4, 2, 12, 1, 1, 6, 2, 2, 4, 2, 8, 6, 2, 2, 120, 2, 4, 6, 1, 2, 12, 2, 2, 6, 28, 2, 1, 2, 2, 6, 4, 2, 4, 2, 2, 3, 2, 2, 24, 2, 4, 6, 4, 2, 6, 14, 8, 6, 4, 10, 4, 2, 7, 18, 5

Offset: 1

Author

Antti Karttunen, Dec 13 2024

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..32769
• Index entries for sequences related to sigma(n).

Crossrefs

Even bisection of A009194.

Topmost row of array A355925.

Cf. A000203, A062731, A378995, A378996.

Cf. also A336850.

Programs

Mathematica

Table[GCD[2n,DivisorSigma[1,2n]],{n,100}] (* James C. McMahon, Dec 14 2024 *)

PARI

A378994(n) = gcd(2*n, sigma(2*n));

Formula

a(n) = A009194(2*n) = gcd(2*n, A062731(n)).

a(n) = 2*n / A378996(n).