344622096domain: NAppears in sequencesa(n) = ( (2^n / n!) * Product_{k=0..n-1} (4*k + 1) )^2.at n=6A127776Binomial(n-k,k)^2 where k = ceiling(n/4).at n=24A171001Binomial coefficients: a(n) = binomial(3*n,n)^2.at n=6A188662