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

1,2

Comments

My comment in A000111 concerning A000111(2*p) mod (2*p) says that all entries are integers.

Links

Table of n, a(n) for n=1..9.

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

Cf. A180418, A000111, A180417.

Sequence in context: A273415 A223055 A308488 * A061888 A348082 A117803

Adjacent sequences: A180416 A180417 A180418 * A180420 A180421 A180422

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