Alternate partial sums of binomial(3*n,n)/(2*n+1).

Terms

a(0) =1a(1) =0a(2) =3a(3) =9a(4) =46a(5) =227a(6) =1201a(7) =6551a(8) =36712a(9) =209963a(10) =1220752a(11) =7193888a(12) =42873220a(13) =257957352a(14) =1564809168a(15) =9559946496a(16) =58768808463a(17) =363261736872