A145470 -id:A145470 - cp's OEIS frontend

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

Leroy Quet, Oct 11 2008

nonn

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

Cf. A145470.

[n:n in [3..1500]| NumberOfDivisors(n-1)+NumberOfDivisors(n-2) eq NumberOfDivisors(n)]; // Marius A. Burtea, May 08 2019

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

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

isok(n) = (n>2) && (numdiv(n) == numdiv(n-1) + numdiv(n-2)); \\ Michel Marcus, May 08 2019

Extended by Emeric Deutsch, Oct 23 2008

Name edited by Jon E. Schoenfield, May 08 2019

A175116 A positive integer k is included if d(k) = d(k+1) * d(k+2), where d(k) is the number of divisors of k.

Original entry on oeis.org

96, 105, 165, 216, 280, 315, 345, 357, 408, 465, 522, 552, 561, 616, 624, 640, 696, 744, 760, 837, 861, 885, 920, 924, 945, 990, 1032, 1056, 1128, 1185, 1281, 1302, 1368, 1386, 1416, 1464, 1560, 1640, 1785, 1830, 1860, 1905, 1950, 2037, 2142, 2184, 2296

Offset: 1

Leroy Quet, Feb 13 2010

nonn

Terms calculated by M. F. Hasler.

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

Cf. A000005, A175115, A145470.

Transpose[Select[Partition[Range[3000],3,1],DivisorSigma[0,First[#]]== DivisorSigma[0,Last[#]]DivisorSigma[0,#[[2]]]&]][[1]]  (* Harvey P. Dale, Apr 08 2011 *)

cp's OEIS Frontend

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

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