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

Terms

a(0) =0a(1) =0a(2) =5a(3) =21a(4) =54a(5) =110a(6) =195a(7) =315a(8) =476a(9) =684a(10) =945a(11) =1265a(12) =1650a(13) =2106a(14) =2639a(15) =3255a(16) =3960a(17) =4760a(18) =5661a(19) =6669a(20) =7790a(21) =9030a(22) =10395a(23) =11891a(24) =13524a(25) =15300a(26) =17225a(27) =19305a(28) =21546a(29) =23954