a(n) = binomial(n+2,3)*5^3.

Terms

a(0) =125a(1) =500a(2) =1250a(3) =2500a(4) =4375a(5) =7000a(6) =10500a(7) =15000a(8) =20625a(9) =27500a(10) =35750a(11) =45500a(12) =56875a(13) =70000a(14) =85000a(15) =102000a(16) =121125a(17) =142500a(18) =166250a(19) =192500a(20) =221375a(21) =253000a(22) =287500a(23) =325000a(24) =365625a(25) =409500a(26) =456750a(27) =507500a(28) =561875a(29) =620000