A281662 (Denominator of Bernoulli(2*n)) read mod n.

0, 0, 0, 2, 1, 0, 6, 6, 6, 0, 6, 6, 6, 2, 12, 14, 6, 12, 6, 10, 0, 8, 6, 18, 16, 4, 15, 2, 6, 0, 6, 30, 9, 30, 31, 30, 6, 30, 3, 10, 6, 0, 6, 30, 3, 30, 6, 42, 6, 30, 42, 30, 6, 30, 33, 6, 42, 30, 6, 30, 6, 30, 42, 62, 1, 24, 6, 30, 42, 50, 6, 6, 6, 30, 72, 30, 61

Offset: 1

Author

Seiichi Manyama, Jan 26 2017

Keywords

• nonn

Comments

Odd terms at: 5, 27, 33, 35, 39, 45, 55, 65, 77, 81, 99, 105, 121, etc. - Robert G. Wilson v, Jan 26 2017

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A002445, A106741, A281648.

Programs

Mathematica

f[n_] := Mod[Denominator[BernoulliB[2 n]], n]; Array[f, 77] (* Robert G. Wilson v, Jan 26 2017 *)

PARI

a(n) = denominator(bernfrac(2*n)) % n; \\ Michel Marcus, Jan 29 2017

Ruby

def bernoulli(n)
  ary = []
  a = []
  (0..n).each{|i|
    a << 1r / (i + 1)
    i.downto(1){|j| a[j - 1] = j * (a[j - 1] - a[j])}
    ary << a[0]
  }
  ary
end
def A281662(n)
  a = bernoulli(2 * n)
  (1..n).map{|i| a[2 * i].denominator % i}
end

Formula

a(n) = A002445(n) mod n.