a(0)=1; a(n) = sigma_1(n) + sigma_3(n).

Terms

a(0) =1a(1) =2a(2) =12a(3) =32a(4) =80a(5) =132a(6) =264a(7) =352a(8) =600a(9) =770a(10) =1152a(11) =1344a(12) =2072a(13) =2212a(14) =3120a(15) =3552a(16) =4712a(17) =4932a(18) =6852a(19) =6880a(20) =9240a(21) =9664a(22) =12024a(23) =12192a(24) =16440a(25) =15782a(26) =19824a(27) =20480a(28) =25168a(29) =24420