Multinomial coefficient n!/ ([n/4]!, [(n+1)/4]!, [(n+2)/4]!, [(n+3)/4]!).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =24a(5) =60a(6) =180a(7) =630a(8) =2520a(9) =7560a(10) =25200a(11) =92400a(12) =369600a(13) =1201200a(14) =4204200a(15) =15765750a(16) =63063000a(17) =214414200a(18) =771891120a(19) =2933186256a(20) =11732745024a(21) =41064607584a(22) =150570227808a(23) =577185873264