OFFSET
1,2
COMMENTS
MATHEMATICA
t = Range[0, 60]! CoefficientList[ Series[ Sec@x + Tan@x, {x, 0, 60}], x]; f[n_] := (Rest[t][[2 Prime@n]] - 1)/(2 Prime@n); Array[f, 9] (* Robert G. Wilson v, Sep 04 2010 *)
PROG
(Python)
from sympy import euler, prime
def A180419(n): return (1-euler(2*(p:=prime(n))))//p>>1 if n > 1 else 1 # Chai Wah Wu, Apr 18 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Sep 03 2010
EXTENSIONS
a(6) onwards from Robert G. Wilson v, Sep 04 2010
Definition rephrased by R. J. Mathar, Sep 29 2010
STATUS
approved