A279623 a(n) = smallest prime factor of n-th Bell number, or 1 if there are none.

1, 1, 2, 5, 3, 2, 7, 877, 2, 3, 5, 2, 37, 27644437, 2, 5, 241, 2, 7, 271, 2, 3, 3, 2, 3, 13, 2, 47, 5, 2, 3, 11, 2, 5694673, 3, 2, 29, 3, 2, 6353, 3221, 2, 35742549198872617291353508656626642567, 3, 2, 5, 5, 2, 3, 7615441337805454611187, 2

Offset: 0

Author

Vincenzo Librandi, Dec 25 2016

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 0..131 (terms 0..100 from Robert G. Wilson v)

Crossrefs

Cf. A000110, A020639, A139044, A144293.

Programs

Magma

[1,1] cat [Minimum(PrimeDivisors(Bell(n))): n in [2..50]];

Mathematica

f[n_] := (FactorInteger@ BellB@ n)[[1, 1]]; Array[f, 50, 0]

Formula

a(n) = A020639(A000110(n)). - Robert Israel, Dec 25 2016