A286359 - OEIS

A286359

Compound filter: a(n) = P(sigma(n), sigma(2n)), where P(n,k) is sequence A000027 used as a pairing function, and sigma is the sum of divisors (A000203).

4, 39, 109, 217, 259, 753, 473, 1005, 1288, 1729, 1093, 3769, 1499, 3105, 4489, 4309, 2503, 8295, 3101, 8557, 8033, 7057, 4489, 16713, 7534, 9633, 12601, 15281, 7051, 28513, 8033, 17829, 18193, 15985, 18193, 40561, 11363, 19761, 24809, 37765, 13903, 50817, 15269, 34537, 48283, 28513, 18193, 70249, 25708, 47679, 41113, 47069, 23059, 79521, 41113, 67281, 50801

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OFFSET

1,1

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Pairing Function

Index entries for sequences related to sigma(n)

FORMULA

a(n) = (1/2)*(2 + ((A000203(n)+A000203(2*n))^2) - A000203(n) - 3*A000203(2*n)).

PROG

(PARI)

A000203(n) = sigma(n);