a(n) = sigma_n(n) - n^n.

Terms

a(0) =0a(1) =1a(2) =1a(3) =17a(4) =1a(5) =794a(6) =1a(7) =65793a(8) =19684a(9) =9766650a(10) =1a(11) =2194095090a(12) =1a(13) =678223089234a(14) =30531927033a(16) =1a(18) =1a(22) =1