a(n) = (7*n^3 + 6*n^2 + 5*n) / 6.

Terms

a(0) =0a(1) =3a(2) =15a(3) =43a(4) =94a(5) =175a(6) =293a(7) =455a(8) =668a(9) =939a(10) =1275a(11) =1683a(12) =2170a(13) =2743a(14) =3409a(15) =4175a(16) =5048a(17) =6035a(18) =7143a(19) =8379a(20) =9750a(21) =11263a(22) =12925a(23) =14743a(24) =16724a(25) =18875a(26) =21203a(27) =23715a(28) =26418a(29) =29319