P(P(n)) - P(P(n-1)), where P(n) = (n+1)*(n+2)*(n+3)/6 (see A000292).

Terms

a(0) =0a(1) =3a(2) =31a(3) =251a(4) =1485a(5) =6665a(6) =24073a(7) =73486a(8) =196626a(9) =473595a(10) =1047255a(11) =2157793a(12) =4189991a(13) =7736001a(14) =13676705a(15) =23285020a(16) =38354788a(17) =61359171a(18) =95642751a(19) =145651815a(20) =217207585a(21) =317827433a(22) =457099401a(23) =647115626a(24) =902970550a(25) =1243330075a(26) =1691078103a(27) =2274047181