a(n) = 1 - sigma(n) + sigma(n)^2 - sigma(n)^3 + sigma(n)^4.

Terms

a(0) =1a(1) =61a(2) =205a(3) =2101a(4) =1111a(5) =19141a(6) =3641a(7) =47461a(8) =26521a(9) =99451a(10) =19141a(11) =593461a(12) =35855a(13) =318505a(14) =318505a(15) =894661a(16) =99451a(17) =2255605a(18) =152381a(19) =3039331a(20) =1016801a(21) =1634221a(22) =318505a(23) =12747541a(24) =894661a(25) =3039331a(26) =2497561a(27) =9661961a(28) =783871a(29) =26505721