a(n) = C(n, Q(n+3, 4)-1)*C(n, Q(n+1, 4)) + C(n, Q(3*n+1, 4))*C(n, Q(3*n+3, 4)) where C = binomial and Q(x, y) = floor(x/y).
A380121
a(n) = C(n, Q(n+3, 4)-1)*C(n, Q(n+1, 4)) + C(n, Q(3*n+1, 4))*C(n, Q(3*n+3, 4)) where C = binomial and Q(x, y) = floor(x/y).
Terms
- a(0) =1a(1) =2a(2) =3a(3) =6a(4) =20a(5) =50a(6) =126a(7) =294a(8) =1008a(9) =2592a(10) =7425a(11) =18150a(12) =62920a(13) =163592a(14) =496860a(15) =1242150a(16) =4331600a(17) =11328800a(18) =35581680a(19) =90140256a(20) =315490896a(21) =828163602a(22) =2658338298a(23) =6793531206a(24) =23836951600a(25) =62728820000a(26) =204451146900a(27) =525731520600
External references
- oeis: A380121