a(n) = binomial(n*(3*n+1)/2, n).

A199747

a(n) = binomial(n*(3*n+1)/2, n).

Terms

    a(0) =1a(1) =2a(2) =21a(3) =455a(4) =14950a(5) =658008a(6) =36288252a(7) =2404808340a(8) =186087894300

External references