A130638 a(n) = 1 iff d(n) = d(n+1), otherwise a(n)=0, where d(n) is the number of divisors of n, A000005.

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, 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, 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

Offset: 1

Author

Giovanni Teofilatto, Aug 11 2007

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000
• Index entries for characteristic functions

Crossrefs

Characteristic function of A005237.

Cf. A000005.

Programs

Mathematica

Table[If[Length[Divisors[n]] == Length[Divisors[n + 1]], 1, 0], {n, 1, 80}] (* Stefan Steinerberger, Aug 12 2007 *)

PARI

A130638(n) = (numdiv(n)==numdiv(n+1)); \\ Antti Karttunen, Oct 04 2017

Extensions

Corrected and extended by Stefan Steinerberger, Aug 12 2007

More terms (up to a(105)) from Antti Karttunen, Oct 04 2017