A130638 - OEIS

%I #15 Oct 04 2017 14:03:13

%S 0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,1,

%T 0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,

%U 0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1,0,0,0,1,0,0,0,0,0,1,0

%N a(n) = 1 iff d(n) = d(n+1), otherwise a(n)=0, where d(n) is the number of divisors of n, A000005.

%H Antti Karttunen, <a href="/A130638/b130638.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%t Table[If[Length[Divisors[n]] == Length[Divisors[n + 1]], 1, 0], {n, 1, 80}] (* _Stefan Steinerberger_, Aug 12 2007 *)

%o (PARI) A130638(n) = (numdiv(n)==numdiv(n+1)); \\ _Antti Karttunen_, Oct 04 2017

%Y Characteristic function of A005237.

%Y Cf. A000005.

%K nonn

%O 1,1

%A _Giovanni Teofilatto_, Aug 11 2007

%E Corrected and extended by _Stefan Steinerberger_, Aug 12 2007

%E More terms (up to a(105)) from _Antti Karttunen_, Oct 04 2017