A071968 Denominators of coefficients of expansion of arctan(x)^2 = x^2-2/3*x^4+23/45*x^6-44/105*x^8+563/1575*x^10-3254/10395*x^12+ ...

1, 1, 3, 45, 105, 1575, 10395, 315315, 45045, 6891885, 72747675, 160044885, 1003917915, 21751554825, 35137127025, 2183521465125, 4512611027925, 76714387474725, 40613499251325, 3172365552631275

Offset

0,3

Links

Table of n, a(n) for n=0..19.

Mathematica

a[n_] := (-1)^(n+1)*Sum[1/(n*(2*k-1)), {k, 1, n}] // Denominator; Table[a[n], {n, 0, 19}] (* Jean-François Alcover, Nov 04 2013 *)

Crossrefs

Cf. A002428.

Sequence in context: A101790 A124494 A075320 * A170921 A093585 A062270

Adjacent sequences: A071965 A071966 A071967 * A071969 A071970 A071971

Keyword

nonn,easy,frac

Author

N. J. A. Sloane, Jun 17 2002

Status

approved