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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

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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