A180419 a(n) = (A000111(2*p) - 1)/(2*p), where p = A000040(n) = prime(n).
1, 10, 5052, 14240070, 3152221563324450, 157195096511273995860, 2374214683408467590063771983920, 618146855974818638210995488847340730, 144946467754033586465978879886385830380958862710
Offset: 1
Keywords
Programs
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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 *) -
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
Extensions
a(6) onwards from Robert G. Wilson v, Sep 04 2010
Definition rephrased by R. J. Mathar, Sep 29 2010
Comments