a(n) = n^phi(n) - 1.

Terms

a(0) =0a(1) =1a(2) =8a(3) =15a(4) =624a(5) =35a(6) =117648a(7) =4095a(8) =531440a(9) =9999a(10) =25937424600a(11) =20735a(13) =7529535a(14) =2562890624a(15) =4294967295a(17) =34012223a(19) =25599999999a(23) =110075314175