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 A057025 #14 Mar 06 2015 23:03:13 %S A057025 2,7,11,29,19,23,53,31,137,1217,43,47,101,109,59,7937,67,71,149,79,83, %T A057025 173,181 %N A057025 Smallest prime of form (2n+1)*2^m+1 for some m. %C A057025 next term a(23) = 47*2^583+1 > 10^177. Sequence then continues: 197, 103, 107, 881, 229, 1889, 977, 127, 131, 269, 139, 569, 293, 151, 617, 317, 163, 167, 1361, 349, 179, 23297, 373, 191, 389, 199, 809, ... %C A057025 If no such prime exists for any m then 2n+1 is called a Sierpiński number. One could use a(n) = 0 for these cases. E.g., a(39278) = 0 because 78557 is a Sierpiński number. For the corresponding numbers m see A046067(n+1), n >= 0, where -1 entries corresponds to a(n) = 0. See also the Sierpiński links there. - _Wolfdieter Lang_, Feb 07 2013 %H A057025 <a href="/index/Pri#riesel">Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime</a> %e A057025 a(5)=23 because 2*5+1=11 and smallest prime of the form 11*2^m+1 is 23 (since 11+1=12 is not prime) %Y A057025 Cf. A032373, A057023, A057026, A046067. %K A057025 nonn %O A057025 0,1 %A A057025 _Henry Bottomley_, Jul 24 2000