A250213 Number of distinct prime factors of A241601(n).

0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 2, 1, 2, 0, 2, 1, 1, 1, 3, 2, 2, 2, 3, 2, 2, 1, 2, 2, 4, 2, 2, 3, 3, 1, 3, 1, 3, 1, 1, 2, 3, 1, 3, 4, 5, 2, 2, 3, 1, 2, 4, 4, 4, 3, 4, 3, 5, 4, 2, 3, 3, 4, 5, 2, 3, 2, 4, 5, 5, 3, 3, 2, 5, 1, 5, 2, 4, 3, 2, 5, 3, 3, 2, 5, 3, 3, 4

Offset: 0

Author

Eric Chen, Dec 28 2014

Keywords

• nonn

Comments

a(n) = 0 iff n is in the set {0, 1, 2, 3, 4, 5, 6, 8, 10, 14};

a(n) = 1 iff n is in A250220.

Crossrefs

Cf. A001221, A241601, A249909, A250214, A250220.

Programs

Mathematica

b[n_] := Numerator[BernoulliB[2 n]/(2 n)];
c[n_] := Numerator[SeriesCoefficient[Log[Tan[x]+1/Cos[x]], {x, 0, 2n+1}]];
a[0] = 0; a[n_] := PrimeNu[If[EvenQ[n], Abs[b[n/2]], c[(n-1)/2]]];
Table[a[n], {n, 0, 78}] (* Jean-François Alcover, Jul 04 2019 *)

Formula

a(n) = A001221(A241601(n)).

Extensions

More terms from Jean-François Alcover, Jul 04 2019

More terms from Jinyuan Wang, Apr 02 2020