A062967 a(n) = 2*(sigma(n)-n-1)+1, where sigma = A000203, sum of divisors of n.

-1, 1, 1, 5, 1, 11, 1, 13, 7, 15, 1, 31, 1, 19, 17, 29, 1, 41, 1, 43, 21, 27, 1, 71, 11, 31, 25, 55, 1, 83, 1, 61, 29, 39, 25, 109, 1, 43, 33, 99, 1, 107, 1, 79, 65, 51, 1, 151, 15, 85, 41, 91, 1, 131, 33, 127, 45, 63, 1, 215, 1, 67, 81, 125, 37, 155, 1, 115, 53, 147, 1, 245, 1, 79, 97, 127, 37, 179, 1, 211, 79, 87, 1, 279, 45, 91, 65

Offset: 1

Author

Jason Earls, Jul 23 2001

Keywords

• easy
• sign

Links

• Antti Karttunen, Table of n, a(n) for n = 1..16384
• Index entries for sequences related to sums of divisors

Crossrefs

Cf. A000203, A001065, A007593.

Programs

Mathematica

Array[2 (DivisorSigma[1, #] - # - 1) + 1 &, 87] (* Michael De Vlieger, Oct 30 2017 *)

PARI

j=[]; for(n=1,200,j=concat(j,2*(sigma(n)-n-1)+1)); j

Formula

a(n) = 2*A001065(n) - 1. - Antti Karttunen, Oct 30 2017