A166123 If n is prime, a(n) = 1; otherwise, a(n) is gcd(n, d) where d is the denominator of the (n-1)-th Bernoulli number.

1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 5, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 15, 1, 1, 1, 7, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 5, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 5, 1, 3, 1, 1, 1, 7, 1, 3, 1, 1, 1, 1, 1, 3, 1

Offset

1,9

Links

Antti Karttunen, Table of n, a(n) for n = 1..21218

Formula

a(n) = A166120(n)/ A050932(n-1).

Mathematica

Table[If[PrimeQ[n], 1, GCD[n, Denominator[BernoulliB[n-1]]]], {n, 100}] (* Harvey P. Dale, Sep 07 2017 *)

Prog

(PARI) a(n)=if(isprime(n), 1, gcd(denominator(bernfrac(n-1)), n)) \\ Charles R Greathouse IV, Jun 20 2011
(PARI) a(n)=my(b=bernfrac(n-1)); denominator(b)/denominator(b*n)/if(isprime(n), n, 1) \\ Charles R Greathouse IV, Jun 20 2011
(PARI) a(n)=if(isprime(n), 1, my(b=bernfrac(n-1)); denominator(b)/denominator(b*n)) \\ Charles R Greathouse IV, Jun 20 2011

Crossrefs

Cf. A166062, A027642.

Sequence in context: A349509 A378645 A262619 * A272334 A014491 A379127

Adjacent sequences: A166120 A166121 A166122 * A166124 A166125 A166126

Keyword

nonn

Author

Paul Curtz, Oct 07 2009

Status

approved