A060780 a(n) = gcd(sigma(n+1), sigma(n)), where sigma = A000203.

1, 1, 1, 1, 6, 4, 1, 1, 1, 6, 4, 14, 2, 24, 1, 1, 3, 1, 2, 2, 4, 12, 12, 1, 1, 2, 8, 2, 6, 8, 1, 3, 6, 6, 1, 1, 2, 4, 2, 6, 6, 4, 4, 6, 6, 24, 4, 1, 3, 3, 2, 2, 6, 24, 24, 40, 10, 30, 12, 2, 2, 8, 1, 1, 12, 4, 2, 6, 48, 72, 3, 1, 2, 2, 4, 4, 24, 8, 2, 1, 1, 42, 28, 4, 12, 12, 60, 90, 18, 2, 56, 8

Offset: 1

Author

Labos Elemer, Apr 26 2001

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A058075.

Programs

Maple

seq(igcd(numtheory:-sigma(n+1),numtheory:-sigma(n)),n=1..100); # Robert Israel, Jul 03 2017

Mathematica

Table[GCD[DivisorSigma[1, n + 1], DivisorSigma[1, n]] , {n, 1, 50}] (* G. C. Greubel, Jul 03 2017 *)

PARI

a(n) = { gcd(sigma(n), sigma(n+1)) } \\ Harry J. Smith, Jul 11 2009

Formula

a(n) = gcd(A000203(n+1), A000203(n)).

Extensions

Name corrected by Robert Israel, Jul 03 2017