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 A128001 #22 May 16 2025 09:51:24 %S A128001 2,3,7,27,51,55,81,1471,1483,8668,10885,20803,32605,36391,57004,61627, %T A128001 88651,89731,133928,153428 %N A128001 Numbers k such that (k-1)*2^k + 1 is prime. %t A128001 Select[Range[200], PrimeQ[(# - 1)*2^# + 1] &] (* _G. C. Greubel_, May 08 2018 *) %o A128001 (PARI) is(n)=ispseudoprime((n-1)<<n+1) \\ _Charles R Greathouse IV_, Jun 06 2017 %Y A128001 Cf. A029544, A002064, A196303. %K A128001 nonn,more %O A128001 1,1 %A A128001 _N. J. A. Sloane_, Jan 25 2008 %E A128001 a(8)-a(14) from _Jason Earls_, Jan 29 2008 %E A128001 a(15)-a(18) from _Charles R Greathouse IV_, Oct 09 2011 %E A128001 a(19)-a(20) from _Michael S. Branicky_, May 14 2025