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A285406 Log base 2 of denominator of Sum_{k=0..n^2-1}((-1)^k*sqrt(Pi)/(Gamma(1/2-k)*Gamma(1+k)))/n). 5
0, 5, 15, 28, 46, 68, 94, 123, 158, 195, 236, 283, 333, 387, 445, 506, 574, 643, 716, 794, 875, 961, 1054, 1146, 1244, 1346, 1451, 1562, 1676, 1794, 1916, 2041, 2174, 2307, 2444, 2586, 2731, 2881, 3034, 3193, 3356, 3520, 3690, 3864, 4041, 4227, 4413, 4601, 4796, 4993 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Needed for studying of Wallis-kind products of central binomials.

LINKS

Table of n, a(n) for n=1..50.

FORMULA

a(n) = A000523(A285389(n)).

a(n) = A056220(n) - A285717(n) = (2*(n^2)) - A007814(n) - A000120(n^2) - 1. - Antti Karttunen, Apr 28 2017, based on Vladimir Shevelev's Jul 20 2009 formula in A000984

MATHEMATICA

Log[2, Table[Denominator[Sum[Binomial[2k, k]/4^k, {k, 0, n^2-1}]/n], {n, 1, 50}]]

Log[2, Denominator[Table[2^(1-2 n^2) n Binomial[2 n^2, n^2], {n, 1, 50}]]] (* Ralf Steiner, Apr 22 2017 *)

PROG

(PARI) a(n) = logint(denominator((2^(1 - 2*(n^2)))*n*binomial(2*(n^2), n^2)), 2); \\ Indranil Ghosh, Apr 27 2017

(PARI) val(n, p) = my(r=0); while(n, r+=n\=p); r

a(n) = 2*n^2-1 - valuation(n, 2) - val(2*n^2, 2) + 2*val(n^2, 2) \\ David A. Corneth, Apr 28 2017

(Python)

from fractions import Fraction

from sympy import binomial

import math

def a(n): return int(round(math.log(Fraction(str(2**(1 - 2*n**2)*n*binomial(2*n**2, n**2))).denominator, 2), 0)) # Indranil Ghosh, Apr 27 2017

(Scheme) (define (A285406 n) (- (* 2 n n) (A007814 n) (A000120 (* n n)) 1)) ;; Antti Karttunen, Apr 28 2017

CROSSREFS

Cf. A000120, A000523, A000984, A007814, A011371, A056220, A201555, A285389, A281264, A285717.

Sequence in context: A110343 A146060 A076843 * A129393 A268581 A298025

Adjacent sequences:  A285403 A285404 A285405 * A285407 A285408 A285409

KEYWORD

nonn

AUTHOR

Ralf Steiner, Apr 18 2017

STATUS

approved

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Last modified October 23 07:20 EDT 2018. Contains 316520 sequences. (Running on oeis4.)