A249909 -id:A249909 - cp's OEIS frontend

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

Eric Chen, Dec 28 2014

nonn

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.

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

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 *)

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

More terms from Jean-François Alcover, Jul 04 2019

More terms from Jinyuan Wang, Apr 02 2020

A250220 Numbers k such that A241601(k) is prime.

Original entry on oeis.org

7, 9, 12, 16, 17, 18, 26, 34, 36, 38, 39, 42, 49, 74, 114, 118, 337, 396, 455

Offset: 1

Eric Chen, Dec 24 2014

Is the sequence infinite?

No other terms < 500. - Jinyuan Wang, Apr 02 2020

Cf. A241601, A249909, A246006, A112548, A092132, A103234.

a(17)-a(19) from Jinyuan Wang, Apr 02 2020

cp's OEIS Frontend

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

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