A145469 - OEIS

%I #25 Sep 08 2022 08:45:38

%S 12,30,40,54,63,75,80,88,135,156,165,174,208,255,260,279,285,318,328,

%T 368,372,405,423,455,460,483,490,495,546,550,552,555,585,654,726,732,

%U 750,795,836,846,870,915,935,940,952,996,1012,1048,1068,1148,1173,1196

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

%H Vaclav Kotesovec, <a href="/A145469/b145469.txt">Table of n, a(n) for n = 1..10000</a>

%p 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

%t Select[Range[1200],DivisorSigma[0,#]==DivisorSigma[0,#-1]+ DivisorSigma[ 0, #-2]&] (* _Harvey P. Dale_, Jan 26 2013 *)

%o (Magma) [n:n in [3..1500]| NumberOfDivisors(n-1)+NumberOfDivisors(n-2) eq NumberOfDivisors(n)]; // _Marius A. Burtea_, May 08 2019

%o (PARI) isok(n) = (n>2) && (numdiv(n) == numdiv(n-1) + numdiv(n-2)); \\ _Michel Marcus_, May 08 2019

%Y Cf. A145470.

%K nonn

%O 1,1

%A _Leroy Quet_, Oct 11 2008

%E Extended by _Emeric Deutsch_, Oct 23 2008

%E Name edited by _Jon E. Schoenfield_, May 08 2019