login
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
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
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
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