Nim-factorial(a(n))=1.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =31a(5) =63a(6) =127a(7) =255a(8) =511a(9) =1023a(10) =2047a(11) =4095a(12) =8191a(13) =16383a(14) =32767a(15) =62914a(16) =65535a(17) =131071a(18) =262143a(19) =524287a(20) =716479a(21) =1048575a(22) =1132639a(23) =2069471a(24) =2097151a(25) =3618111a(26) =4194303a(27) =8388607