A045762 Numbers k such that 2^k - 1 is not a prime.
0, 1, 4, 6, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 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, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79
Offset: 1
Examples
8 belongs to the sequence because 2^8 - 1 = 255 is not a prime.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Magma
[n: n in [0..100]| not IsPrime(2^n-1)]; // Vincenzo Librandi, Jan 28 2011
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Mathematica
Select[Range[0,100],!PrimeQ[2^#-1]&] (* Harvey P. Dale, Mar 22 2011 *)
Formula
Complement of A000043.
Extensions
More terms from Jennifer D. Secor (s1175994(AT)cedarville.edu)