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A275711 Nearest integer to 2*n!*(2/Pi)^(n+1). 1
1, 1, 1, 2, 5, 16, 61, 272, 1385, 7936, 50521, 353791, 2702767, 22368251, 199360995, 1903757268, 19391512295, 209865342434, 2404879677510, 29088885104489, 370371188272931, 4951498052966308, 69348874393874527, 1015423886503257017, 15514534163575397655 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

For n odd, approximation to the tangent (or "Zag") numbers A000182. For n even, approximation to the secant (or "Zig") numbers A000364. The first difference from the Euler (or "up/down") numbers A000111 occurs for a(11)=353791 /= A000111(11)=353792.

LINKS

Hugo Pfoertner, Table of n, a(n) for n = 0..100

P. Flajolet and R. Sedgewick, Analytic Combinatorics, Cambridge University Press, 2009, pages 2-5.

FORMULA

a(n) = round (2*n!*(2/Pi)^(n+1)).

MATHEMATICA

Table[Round[2*n!*(2/Pi)^(n+1)], {n, 0, 30}] (* Harvey P. Dale, Jun 18 2017 *)

CROSSREFS

Cf. A000111, A000182, A000364.

Sequence in context: A303058 A178123 A138265 * A163747 A000111 A007976

Adjacent sequences:  A275708 A275709 A275710 * A275712 A275713 A275714

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Aug 06 2016

STATUS

approved

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Last modified November 20 23:03 EST 2018. Contains 317427 sequences. (Running on oeis4.)