A089626 a(n) = 1/h(n) where {h(n)} is the Hankel transform of {t(n)}; t(n) is defined by the expansion of tan(x)= Sum_n>0, t(n)*x^(2*n-1); |x|<Pi/2.

1, 45, 4465125, 6272287562165625, 438120013555654794702228515625, 3943988517696329309474874414036059896739501953125, 9860368980530253649041813027973243717504383071655695011832599639892578125

Offset

1,2

Comments

t(n)= (2^(2*n)-1)*2^(2*n)*B_n /(2*n)! B_n: numbers of Bernoulli, sequence 1/6, 1/30, 1/42, 1/30, 5/66, ... example:n=2, a(2)= 1/det|1, 1/3|1/3, 2/15|= 1/(1/45)=45 See A001906 for the definition of Hankel transform.

Links

Table of n, a(n) for n=1..7.

Formula

a(n) = (4*n-3)^1*(4*n-5)^2*...*3^(2*n-2)*1^(2*n-1).

a(n) = A057863(2*n-1). - Vaclav Kotesovec, Oct 16 2015

Crossrefs

Cf. A057863.

Sequence in context: A003739 A300198 A145319 * A110479 A023934 A022076

Adjacent sequences: A089623 A089624 A089625 * A089627 A089628 A089629

Keyword

easy,nonn

Author

Philippe Deléham, Dec 31 2003

Status

approved