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 A007647 M2783 #20 Mar 22 2024 19:38:18 %S A007647 1,3,9,21,363,2161,4839,49521,105994,207777 %N A007647 Numbers k such that k*10^k + 1 is prime. %C A007647 These are generalized Cullen numbers in base 10. - Julien Peter Benney (jpbenney(AT)ftml.net), Oct 24 2004 %C A007647 No others less than 270026. - _Ray Chandler_, Apr 10 2016 %D A007647 J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 363, p. 84, Ellipses, Paris 2008. %D A007647 H. Dubner, Generalized Cullen numbers, J. Rec. Math., 21 (No. 3, 1989), 190-191. %D A007647 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A007647 Daniel Hermle, <a href="http://www.primzahlenarchiv.de/primes10.html">First Coordinated Generalized Cullen Prime Search</a>. %H A007647 Guenter Loeh, <a href="http://guenter.loeh.name/gc/status.html">Generalized Cullen primes</a>. %e A007647 For k = 3 we get (3*10^3)+1 = (3*1000)+1 = 3000 + 1 = 3001, which is prime. %e A007647 For k = 9 we get 9*10^9+1 = 9*1000000000+1 = 9000000000+1 = 9000000001, which is prime. %o A007647 (PARI) is(n)=ispseudoprime(n*10^n+1) \\ _Charles R Greathouse IV_, Feb 17 2017 %Y A007647 Cf. A004023. %K A007647 hard,nonn %O A007647 1,2 %A A007647 _N. J. A. Sloane_ %E A007647 More terms from Julien Peter Benney (jpbenney(AT)ftml.net), Jun 11 2005 %E A007647 Edited by _N. J. A. Sloane_ at the suggestion of _Andrew S. Plewe_, Jun 05 2007 %E A007647 a(10) from Loeh link by _Ray Chandler_, Apr 10 2016