A172969 Numbers k such that 3*A000005(k) = 2*A000005(k+1).

3, 27, 51, 62, 74, 91, 99, 115, 123, 146, 187, 206, 235, 267, 274, 278, 291, 351, 355, 362, 386, 403, 411, 422, 427, 451, 459, 494, 538, 584, 665, 667, 721, 723, 746, 763, 771, 824, 843, 854, 866, 875, 926, 955, 987, 1003, 1027, 1034, 1057, 1070, 1082

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 A074775.

Cf. A000005, A172624.

Programs

Maple

for n from 1 to 1100 do if 3*numtheory[tau](n) = 2*numtheory[tau](n+1) then  printf("%d,",n) ; end if; end do:

Mathematica

Select[Range[1200], 3*DivisorSigma[0, #] == 2*DivisorSigma[0, # + 1] &] (* Amiram Eldar, Apr 09 2024 *)

PARI

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

Formula

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