A062835 a(1) = 0; for n > 1 a(n) = sum of divisors of n^2-1; or sigma(A005563(n-1)).

0, 4, 15, 24, 60, 48, 124, 104, 186, 156, 360, 168, 480, 336, 504, 432, 819, 360, 1170, 640, 1080, 768, 1488, 744, 1736, 1240, 1680, 1200, 2880, 960, 3048, 1536, 2286, 2304, 3510, 1824, 3900, 2128, 3720, 2352, 5952, 1848, 5760, 3432, 4320, 3744, 6048

Offset: 1

Author

Jason Earls, Jul 21 2001

Keywords

• easy
• nonn

Links

• Metin Sariyar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)

Crossrefs

Cf. A000203, A005563.

Programs

GAP

Concatenation([0], List([2..100], n-> Sigma(n^2 -1) )); # G. C. Greubel, Dec 31 2019

Magma

[0] cat [DivisorSigma(1, n^2 -1): n in [2..100]]; // G. C. Greubel, Dec 31 2019

Maple

with(numtheory): seq( `if`(n=1, 0, sigma(n^2 -1)), n=1..100); # G. C. Greubel, Dec 31 2019

Mathematica

Table[If[n==1,0,DivisorSigma[1, n^2 - 1]], {n, 120}] (* corrected by Metin Sariyar, Dec 12 2019 *)

PARI

a(n)={if(n<2, 0, sigma(n^2 - 1))}

Sage

[0]+[sigma(n^2 -1, 1) for n in (2..100)] # G. C. Greubel, Dec 31 2019

Formula

Sum_{k=1..n} a(k) = (35/48) * n^3 + O((n*log(n))^2). - Amiram Eldar, Dec 09 2024

Extensions

Name corrected by Omar E. Pol, Dec 08 2019