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 A167576 The first column of the ED3 array A167572. 9
 1, 5, 23, 167, 1473, 16413, 211479, 3192975, 54010305, 1030249845, 21566327895, 497334999735, 12405876372225, 335591130336525, 9716331072597975, 301633179343890975, 9941514351641143425, 348336799875365041125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Basically a(n) measures the difference between the Euler factorial n! and the Luschny factorial L(n) at half integer values. For the Luschny factorial see the link. The formula given in the Maple section is a variant of a formula given by Cyril Damamme in A135457. - Peter Luschny, Jul 18 2015 LINKS G. C. Greubel, Table of n, a(n) for n = 1..400 FORMULA a(n) = (-1)^(n)*(2*n-3)!!*((1)+(4*n-2)*sum((-1)^(k+n)/(2*k+1), k=0..n-1)) a(n) = (2*n-1)*a(n-1)+2*(-1)^n*(2*n-5)!! with a(1) = 1. a(n) = 4*a(n-1)+(4*n^2-16*n+15)*a(n-2) with a(1) = 1 and a(2) = 5 [Superseeker]. 0 = a(n)*a(n+1)*(-440*a(n+2) - 220*a(n+3) + 55*a(n+4)) + a(n)*a(n+2)*(536*a(n+2) - 118*a(n+3) - 4*a(n+4)) + a(n)*a(n+3)*(-4*a(n+3) + a(n+4)) + a(n+1)^2*(-220*a(n+2) - 32*a(n+3) + 8*a(n+4)) + a(n+1)*a(n+2)*(+71*a(n+2) + 4*a(n+3) - 2*a(n+4)) + a(n+2)^2*(-4*a(n+2) + a(n+3)) if n>0. - Michael Somos, Jul 19 2015 a(n) = (-1+(n-1/2)*LerchPhi(-1,1,n+1/2)+(-n+1/2)*LerchPhi(-1,1,-n+1/2))/(1-2*n)!!. - Johannes W. Meijer, Jul 20 2015 a(n) = A024199(n) + A135457(n). - Cyril Damamme, Jul 22 2015 a(n) = ((-1)^n/(2 n - 1) + Pi/2 - (-1)^n LerchPhi(-1, 1, n + 1/2)) (2 n - 1)!!. - Michael Somos, Jan 31 2019 EXAMPLE G.f. = x + 5*x^2 + 23*x^3 + 167*x^4 + 1473*x^5 + 16413*x^6 + ... MAPLE L := x -> (1+x*(Psi(1-x/2)-Psi(1/2-x/2)))/(-x)!: a := x -> (L(x-1/2)-(x-1/2)!)*2^(x-1)*sqrt(Pi): seq(simplify(a(n)), n=1..18); # Peter Luschny, Jul 18 2015 a := proc(n) option remember: if n=1 then 1 else (2*n-1)*a(n-1)+2*(-1)^n*doublefactorial(2*n-5) fi: end: seq(a(n), n=1..18); # Johannes W. Meijer, Jul 20 2015 MATHEMATICA a[ n_] := If[ n < 1, 0, (2 n - 3)!! ((-1)^n - I (4 n - 2) Sum[ I^k / k, {k, 1, 2 n - 1, 2}])]; (* Michael Somos, Jul 20 2015 *) a[ n_] := If[ n < 1, 0, (2 n - 3)!! ((-1)^n + (4 n - 2) Sum[ KroneckerSymbol[ -4, k]/ k, {k, 2 n - 1}])]; (* Michael Somos, Jan 31 2019 *) PROG (PARI) {a(n) = if( n<1, 0, prod(k=1, n-1, 2*k - 1) * ((-1)^n - (4*n - 2) * sum(k=1, n, (-1)^k / (2*k - 1))))}; /* Michael Somos, Jul 20 2015 */ CROSSREFS Equals the first column of the ED3 array A167572. Equals the first right hand column of A167583. Other columns are A167577 and A167578. Cf. A097801 (the 2*(-1)^n*(2*n-5)!! factor). Cf. A007509 and A025547 (the sum((-1)^(k+n)/(2*k+1), k=0..n-1) factor). Cf. A024199 and A135457. Sequence in context: A054749 A107204 A178383 * A306180 A308443 A116151 Adjacent sequences:  A167573 A167574 A167575 * A167577 A167578 A167579 KEYWORD easy,nonn AUTHOR Johannes W. Meijer, Nov 10 2009 STATUS approved

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Last modified September 18 01:39 EDT 2021. Contains 347504 sequences. (Running on oeis4.)