a(n) = sigma_2(n)^2.

Terms

a(0) =1a(1) =25a(2) =100a(3) =441a(4) =676a(5) =2500a(6) =2500a(7) =7225a(8) =8281a(9) =16900a(10) =14884a(11) =44100a(12) =28900a(13) =62500a(14) =67600a(15) =116281a(16) =84100a(17) =207025a(18) =131044a(19) =298116a(20) =250000a(21) =372100a(22) =280900a(23) =722500a(24) =423801a(25) =722500a(26) =672400a(27) =1102500a(28) =708964a(29) =1690000