A123927 - OEIS

%I #14 Nov 22 2017 20:47:58

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

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

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

%N Characteristic function of natural numbers with number of divisors equal to a Lucas number.

%H Antti Karttunen, <a href="/A123927/b123927.txt">Table of n, a(n) for n = 1..65537</a>

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

%H <a href="/index/Eu#epf">Index entries for sequences computed from exponents in factorization of n</a>

%F a(n) = A102460(A000005(n)). - _Antti Karttunen_, Nov 22 2017

%t With[{nn = 103}, Table[Boole[MemberQ[#, DivisorSigma[0, n]]], {n, nn}] &@ TakeWhile[Union@ Array[LucasL, 40, 0], # <= nn &]] (* _Michael De Vlieger_, Nov 22 2017 *)

%o (PARI)

%o A102460(n) = { my(u1=1,u2=3,old_u1); if(n<=2,sign(n),while(n>u2,old_u1=u1;u1=u2;u2=old_u1+u2);(u2==n)); };

%o A123927(n) = A102460(numdiv(n)); \\ _Antti Karttunen_, Nov 22 2017

%Y Cf. A000005, A102460, A119885, A119911, A122895.

%K easy,nonn

%O 1,1

%A _Giovanni Teofilatto_, Nov 22 2006

%E Superfluous 0 at the beginning of data removed by _Antti Karttunen_, Nov 22 2017