A transform of C(n,3).

Terms

a(0) =1a(1) =4a(2) =20a(3) =80a(4) =280a(5) =896a(6) =2688a(7) =7680a(8) =21120a(9) =56320a(10) =146432a(11) =372736a(12) =931840a(13) =2293760a(14) =5570560a(15) =13369344a(16) =31752192a(17) =74711040a(18) =174325760a(19) =403701760a(20) =928514048a(21) =2122317824a(22) =4823449600a(23) =10905190400a(24) =24536678400a(25) =54962159616a(26) =122607894528