a(n) = binomial(6*n,3*n).A066802a(n) = binomial(6*n,3*n).Terms a(0) =1a(1) =20a(2) =924a(3) =48620a(4) =2704156a(5) =155117520a(6) =9075135300a(7) =538257874440External referencesoeis: A066802