This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A045762 #27 Oct 22 2024 05:41:56 %S A045762 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, %T A045762 33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55, %U A045762 56,57,58,59,60,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79 %N A045762 Numbers k such that 2^k - 1 is not a prime. %H A045762 Amiram Eldar, <a href="/A045762/b045762.txt">Table of n, a(n) for n = 1..10000</a> %F A045762 Complement of A000043. %e A045762 8 belongs to the sequence because 2^8 - 1 = 255 is not a prime. %t A045762 Select[Range[0,100],!PrimeQ[2^#-1]&] (* _Harvey P. Dale_, Mar 22 2011 *) %o A045762 (Magma) [n: n in [0..100]| not IsPrime(2^n-1)]; // _Vincenzo Librandi_, Jan 28 2011 %Y A045762 Cf. A000043 (Mersenne prime exponents), A054723 (primes of this sequence). %K A045762 nonn,easy,nice %O A045762 1,3 %A A045762 _Felice Russo_ %E A045762 More terms from Jennifer D. Secor (s1175994(AT)cedarville.edu)