Second elementary symmetric function of the first n terms of (2,2,3,3,4,4,5,5...).

Terms

a(0) =4a(1) =16a(2) =37a(3) =77a(4) =133a(5) =223a(6) =338a(7) =506a(8) =710a(9) =990a(10) =1319a(11) =1751a(12) =2247a(13) =2877a(14) =3588a(15) =4468a(16) =5448a(17) =6636a(18) =7945a(19) =9505a(20) =11209a(21) =13211a(22) =15382a(23) =17902a(24) =20618a(25) =23738a(26) =27083a(27) =30891a(28) =34955a(29) =39545