A145469 Positive integers k such that d(k) = d(k-1) + d(k-2), where d(k) is the number of divisors of k.

12, 30, 40, 54, 63, 75, 80, 88, 135, 156, 165, 174, 208, 255, 260, 279, 285, 318, 328, 368, 372, 405, 423, 455, 460, 483, 490, 495, 546, 550, 552, 555, 585, 654, 726, 732, 750, 795, 836, 846, 870, 915, 935, 940, 952, 996, 1012, 1048, 1068, 1148, 1173, 1196

Offset

1,1

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..10000

Maple

with(numtheory): a:=proc(n) if tau(n)=tau(n-1)+tau(n-2) then n else end if end proc: seq(a(n), n=3..1300); # Emeric Deutsch, Oct 23 2008

Mathematica

Select[Range[1200], DivisorSigma[0, #]==DivisorSigma[0, #-1]+ DivisorSigma[ 0, #-2]&] (* Harvey P. Dale, Jan 26 2013 *)

Prog

(Magma) [n:n in [3..1500]| NumberOfDivisors(n-1)+NumberOfDivisors(n-2) eq NumberOfDivisors(n)]; // Marius A. Burtea, May 08 2019
(PARI) isok(n) = (n>2) && (numdiv(n) == numdiv(n-1) + numdiv(n-2)); \\ Michel Marcus, May 08 2019

Crossrefs

Cf. A145470.

Sequence in context: A083096 A307348 A289691 * A024364 A093507 A325802

Adjacent sequences: A145466 A145467 A145468 * A145470 A145471 A145472

Keyword

nonn

Author

Leroy Quet, Oct 11 2008

Extensions

Extended by Emeric Deutsch, Oct 23 2008

Name edited by Jon E. Schoenfield, May 08 2019

Status

approved