A322569 - OEIS

A322569

a(n)=x is the least integer such that gcd(sigma(x), sigma(x+1)) = 2*n.

13, 6, 5, 27, 57, 22, 12, 93, 89, 236, 1032, 14, 467, 83, 58, 308, 201, 118, 147, 56, 82, 1204, 6301, 69, 596, 1142, 106, 91, 4167, 87, 432, 381, 393, 1407, 348, 70, 5912, 453, 233, 417, 13692, 166, 56493, 1118, 88, 6987, 54048, 154, 1843, 4490, 6833, 2574, 633, 689, 1538

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OFFSET

1,1

COMMENTS

Bisection of A084307.

LINKS

Michel Marcus, Table of n, a(n) for n = 1..1000

MATHEMATICA

Module[{nn=60000, g}, g=GCD@@@Partition[DivisorSigma[1, Range[nn]], 2, 1]; Table[ Position[ g, 2n, 1, 1], {n, 55}]]//Flatten (* Harvey P. Dale, Jan 28 2023 *)

PROG

(PARI) a(n) = my(x=1); while(gcd(sigma(x), sigma(x+1)) != 2*n, x++); x;

(Magma) sol:=[]; for n in [1..55] do k:=1; while Gcd(DivisorSigma(1, k), DivisorSigma(1, k+1)) ne 2*n do k:=k+1; end while; Append(~sol, k); end for; sol; // Marius A. Burtea, Aug 29 2019

CROSSREFS

Cf. A000203, A060780, A084307.

Sequence in context: A296438 A010217 A033333 * A004478 A300504 A168210

Adjacent sequences: A322566 A322567 A322568 * A322570 A322571 A322572

KEYWORD

nonn

AUTHOR

Michel Marcus, Aug 29 2019

STATUS

approved