A138888 Non-Fermat numbers.

1, 2, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73

Offset: 1

Author

Omar E. Pol, Apr 03 2008

Keywords

• easy
• nonn

Comments

Numbers that are not members of A000215.

Crossrefs

Cf. A000215, A001690, A018252.

Programs

Mathematica

Complement[Range[10000],{3,5,17,257}] (* Harvey P. Dale, Aug 04 2023 *)

Python

def A138888(n): return n+(m:=((n-1).bit_length()-1).bit_length() if n>2 else 0)+(n+m>=(1<<(1<Chai Wah Wu, Oct 19 2024

Formula

For n > 2, a(n) = n+m+2 if n+m>=4^(2^m) and a(n) = n+m+1 otherwise where m = floor(log_2(log_2(n-1))). - Chai Wah Wu, Oct 19 2024