a(n) = 1 + 21 n + 168 n^2 + 588 n^3 + 1029 n^4.

Terms

a(0) =1a(1) =1807a(2) =21883a(3) =100801a(4) =303829a(5) =720931a(6) =1466767a(7) =2680693a(8) =4526761a(9) =7193719a(10) =10895011a(11) =15868777a(12) =22377853a(13) =30709771a(14) =41176759a(15) =54115741a(16) =69888337a(17) =88880863a(18) =111504331a(19) =138194449a(20) =169411621a(21) =205640947a(22) =247392223a(23) =295199941