a(n) = floor(n*(n^3-n-3)/(2*(n-1))).

Terms

a(0) =3a(1) =15a(2) =38a(3) =73a(4) =124a(5) =194a(6) =286a(7) =403a(8) =548a(9) =724a(10) =934a(11) =1181a(12) =1468a(13) =1798a(14) =2174a(15) =2599a(16) =3076a(17) =3608a(18) =4198a(19) =4849a(20) =5564a(21) =6346a(22) =7198a(23) =8123a(24) =9124a(25) =10204a(26) =11366a(27) =12613a(28) =13948a(29) =15374