a(n) = n + n*(n-1)*(n-2)*(n-3).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =28a(5) =125a(6) =366a(7) =847a(8) =1688a(9) =3033a(10) =5050a(11) =7931a(12) =11892a(13) =17173a(14) =24038a(15) =32775a(16) =43696a(17) =57137a(18) =73458a(19) =93043a(20) =116300a(21) =143661a(22) =175582a(23) =212543a(24) =255048a(25) =303625a(26) =358826a(27) =421227a(28) =491428a(29) =570053