A355452 - OEIS

%I #11 Apr 22 2023 14:41:37

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

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

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

%N a(n) = 1 if Bernoulli number B_{n} has denominator 6, otherwise 0.

%H Antti Karttunen, <a href="/A355452/b355452.txt">Table of n, a(n) for n = 1..100000</a>

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

%F a(n) = 1 if A027642(n) = 6, otherwise 0.

%F a(n) = 1 if A067513(n) = 2, otherwise 0.

%F For n > 2, a(n) <= A355451(n).

%t Table[If[Denominator[BernoulliB[n]]==6,1,0],{n,130}] (* _Harvey P. Dale_, Apr 22 2023 *)

%o (PARI) A355452(n) = (6==denominator(bernfrac(n)));

%o (PARI) A355452(n) = if(n%2, 0, fordiv(n/2, d, if(isprime(2*d+1)&&d>1, return(0))); (1)); \\ After function "is" in A051222

%Y Characteristic function of A051222.

%Y Cf. A027642, A067513, A355451.

%K nonn

%O 1

%A _Antti Karttunen_, Jul 12 2022