a(n) = gcd(n! mod 2^n, (n+1)! mod 2^(n+1)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =8a(5) =8a(6) =16a(7) =16a(8) =128a(9) =384a(10) =256a(11) =256a(12) =3072a(13) =1024a(14) =2048a(15) =2048a(16) =32768a(17) =98304a(18) =65536a(19) =65536a(20) =262144a(21) =262144a(22) =524288a(23) =524288a(24) =4194304a(25) =4194304a(26) =8388608a(27) =8388608a(28) =33554432a(29) =33554432