A172624 Numbers k such that 2*A000005(k) = 3*A000005(k+1).

4, 20, 32, 45, 50, 68, 76, 92, 117, 124, 212, 236, 261, 325, 333, 338, 350, 412, 436, 452, 477, 578, 596, 608, 620, 628, 644, 650, 668, 716, 722, 740, 788, 801, 804, 825, 836, 855, 860, 884, 892, 916, 925, 932, 964, 968, 981, 1014, 1017, 1058, 1076

Offset: 1

Author

Juri-Stepan Gerasimov, Nov 21 2010

Keywords

• nonn

Links

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

Crossrefs

Subsequence of A059269.

Cf. A000005, A172969.

Programs

Mathematica

Select[Range[1100],2*DivisorSigma[0,#]==3*DivisorSigma[0,#+1]&] (* Harvey P. Dale, Nov 06 2012 *)

PARI

is(n) = 2 * numdiv(n) == 3 * numdiv(n+1); \\ Amiram Eldar, Apr 09 2024

Formula

{k: 2*tau(k) = 3*tau(k+1)}.

Extensions

Corrected by D. S. McNeil, Nov 21 2010