a(n) = floor((3rd elementary symmetric function of 2,3,...,n+3)/(2+3+...+n+3)).

Terms

a(0) =2a(1) =11a(2) =29a(3) =61a(4) =115a(5) =196a(6) =312a(7) =474a(8) =690a(9) =971a(10) =1331a(11) =1781a(12) =2335a(13) =3010a(14) =3820a(15) =4782a(16) =5916a(17) =7239a(18) =8771a(19) =10535a(20) =12551a(21) =14842a(22) =17434a(23) =20350a(24) =23616a(25) =27261a(26) =31311a(27) =35795a(28) =40745a(29) =46190