a(n) = 5*n^2.

Terms

a(0) =0a(1) =5a(2) =20a(3) =45a(4) =80a(5) =125a(6) =180a(7) =245a(8) =320a(9) =405a(10) =500a(11) =605a(12) =720a(13) =845a(14) =980a(15) =1125a(16) =1280a(17) =1445a(18) =1620a(19) =1805a(20) =2000a(21) =2205a(22) =2420a(23) =2645a(24) =2880a(25) =3125a(26) =3380a(27) =3645a(28) =3920a(29) =4205