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A066294 a(n) = A000203(n)^2 - A001157(n) - 2n = sigma(n)^2 - sigma_2(n) - 2n. 1
-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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A000203, A001157.

Sequence in context: A120582 A003784 A244143 * A230840 A209454 A287713

Adjacent sequences:  A066291 A066292 A066293 * A066295 A066296 A066297

KEYWORD

sign

AUTHOR

Labos Elemer, Dec 12 2001

STATUS

approved

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Last modified July 26 10:35 EDT 2021. Contains 346294 sequences. (Running on oeis4.)