A180417 a(n) = (A000111(2^n) - 1) / 2^n.

0, 0, 1, 173, 1211969509, 5547480986860602794895774677, 708720364531529518355420122993246286974247836241724513772950684967495246261

Offset: 0

Author

Vladimir Shevelev, Sep 03 2010

Keywords

• nonn

Comments

The definition yields integers according to the formula in A000111.

The next term a(7) is too large to include. - N. J. A. Sloane, Mar 14 2011

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..8

Crossrefs

Cf. A000079, A000111.

Programs

Mathematica

t = Range[0, 65]! CoefficientList[ Series[ Sec@x + Tan@x, {x, 0, 65}], x]; f[n_] := (Rest[t][[2^n]] - 1)/2^n; Array[f, 7, 0] (* Robert G. Wilson v, Sep 04 2010 *)

Python

from sympy import euler
def A180417(n): return euler(1<>n if n > 1 else 0 # Chai Wah Wu, Apr 18 2023

Extensions

Two more terms from R. J. Mathar, Sep 19 2010

a(5) and a(6) from Robert G. Wilson v, Sep 04 2010