A090947 Largest prime factor of numerator of Bernoulli(2n) (or 1 if the numerator is 1).

1, 1, 1, 1, 1, 5, 691, 7, 3617, 43867, 617, 593, 2294797, 657931, 362903, 1001259881, 305065927, 151628697551, 26315271553053477373, 154210205991661, 1897170067619, 1520097643918070802691, 1798482437, 67568238839737, 153289748932447906241, 47464429777438199, 4534045619429, 1120412849144121779, 19088082706840550550313, 37349583369104129, 109317926249509865753025015237911, 28765594733083851481, 87057315354522179184989699791727, 159562251828620181390358590156239282938769, 5525473366510930028227481

Offset: 0

Author

N. J. A. Sloane, Feb 28 2004

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 0..103

Crossrefs

Cf. A000367, A006530, A079294.

Programs

Mathematica

PrimeFactors[ n_] := Flatten[ Table[ #[[1]], {1} ] & /@ FactorInteger[ n ]]; A090947[n_] := PrimeFactors[ Numerator[ BernoulliB[2n]]][[ -1]]; Table[ A090947[n], {n, 5, 24}] (* Robert G. Wilson v, Feb 28 2004 *)

Formula

a(n) = A006530(abs(A000367(n))). - Amiram Eldar, Feb 09 2020

Extensions

More terms from Robert G. Wilson v and Hans Havermann, Feb 28 2004