6n*(6n-1)*(6n-2)*(6n-3)*(6n-4)*(6n-5).

Terms

a(0) =0a(1) =720a(2) =665280a(3) =13366080a(4) =96909120a(5) =427518000a(6) =1402410240a(7) =3776965920a(8) =8835488640a(9) =18595558800a(10) =36045979200a(11) =65418312960a(12) =112492013760a(13) =184933148400a(14) =292666711680a(15) =448282533600a(16) =667474778880a(17) =969515038800