A179931 a(n) = gcd(sigma(n), sigma_2(n)).

1, 1, 2, 7, 2, 2, 2, 5, 13, 2, 2, 14, 2, 2, 4, 31, 2, 13, 2, 42, 4, 2, 2, 10, 31, 2, 20, 14, 2, 4, 2, 21, 4, 2, 4, 91, 2, 10, 4, 10, 2, 4, 2, 42, 26, 2, 2, 62, 57, 93, 4, 14, 2, 20, 4, 10, 20, 10, 2, 84, 2, 2, 26, 127, 4, 4, 2, 42, 4, 4, 2, 65, 2, 2, 62, 14, 4, 4, 2, 62, 121, 2, 2, 28, 4, 2, 20, 10, 2, 26, 4, 42, 4, 2, 4, 42, 2, 57, 26, 217

Offset

1,3

Comments

A006530(a(n)) = A082066(n). - Reinhard Zumkeller, Jul 10 2011, the latter A-number corrected by Antti Karttunen, May 22 2017.

Not multiplicative: a(2)*a(19) <> a(38). - R. J. Mathar, Oct 08 2011

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Maple

A179931 := proc(n) igcd( numtheory[sigma](n), numtheory[sigma][2](n)) ; end proc:
seq(A179931(n), n=1..100) ;

Mathematica

Table[GCD @@ Map[DivisorSigma[#, n] &, {1, 2}], {n, 100}] (* Michael De Vlieger, May 22 2017 *)

Prog

(PARI) a(n)=gcd(sigma(n), sigma(n, 2)) \\ Charles R Greathouse IV, Feb 14 2013

Crossrefs

Cf. A179930, A000203, A001157, A082066, A009194.

Sequence in context: A195476 A082072 A082066 * A130335 A347236 A073246

Adjacent sequences: A179928 A179929 A179930 * A179932 A179933 A179934

Keyword

nonn

Author

N. J. A. Sloane, Jul 09 2011, following a suggestion from R. J. Mathar

Status

approved