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A138888
Non-Fermat numbers.
6
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
1,2
COMMENTS
Numbers that are not members of A000215.
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
MATHEMATICA
Complement[Range[10000], {3, 5, 17, 257}] (* Harvey P. Dale, Aug 04 2023 *)
PROG
(Python)
def A138888(n): return n+(m:=((n-1).bit_length()-1).bit_length() if n>2 else 0)+(n+m>=(1<<(1<<m))+1) # Chai Wah Wu, Oct 19 2024
CROSSREFS
KEYWORD
easy,nonn,changed
AUTHOR
Omar E. Pol, Apr 03 2008
STATUS
approved