OFFSET
1,4
LINKS
Michael Hardy, A "known" tangent half-angle formula?.
FORMULA
EXAMPLE
1; 1, 1; 3, 25, 3; 17, 329, 329, 17; ...
PROG
(PARI) {T(n, k) = local(u = 'u, v = 'v, A); if( n<0 || k>=n, 0, n = 2*n; k = 2*k + 1; A = x * O(x^n); n! * polcoeff( polcoeff( polcoeff( sin( u*x + A) * sin( v*x + A) / (cos( u*x + A) + cos( v*x + A)), n, x), k, u), n - k, v))}
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Michael Somos, Jul 23 2013
STATUS
approved