A066294 a(n) = A000203(n)^2 - A001157(n) - 2n = sigma(n)^2 - sigma_2(n) - 2n.

-2, 0, 0, 20, 0, 82, 0, 124, 60, 174, 0, 550, 0, 298, 286, 588, 0, 1030, 0, 1178, 482, 642, 0, 2702, 260, 862, 726, 2030, 0, 3824, 0, 2540, 1018, 1398, 934, 6298, 0, 1714, 1358, 5810, 0, 6632, 0, 4406, 3628, 2442, 0, 11870, 700, 5294, 2182, 5930, 0, 10192, 1902, 10038, 2666, 3774, 0, 22644, 0, 4282, 6140, 10540, 2506

Offset: 1

Author

Labos Elemer, Dec 12 2001

Keywords

• sign

Comments

For primes p, a(p) = 0, otherwise positive, except for n = 1 where it is negative.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A001157.

Programs

Mathematica

a[n_] := DivisorSigma[1,n]^2 - DivisorSigma[2,n] - 2n; Array[a, 65] (* Amiram Eldar, Jul 31 2019 *)

PARI

a(n) = sigma(n)^2 - sigma(n, 2) - 2*n; \\ Michel Marcus, Mar 22 2020