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 A259866 #17 Jan 28 2023 08:02:36 %S A259866 31,3001,30000001,30000000001,30000000000000000000000000001, %T A259866 3000000000000000000000000000000000001, %U A259866 30000000000000000000000000000000000000000000000000000000000000000001 %N A259866 Primes of the form 3*10^k + 1. %H A259866 S. W. Golomb, <a href="http://www.jstor.org/stable/2005337">Properties of the sequence 3.2^n+1</a>, Math. Comp., 30 (1976), 657-663. %H A259866 S. W. Golomb, <a href="/A004119/a004119.pdf">Properties of the sequence 3.2^n+1</a>, Math. Comp., 30 (1976), 657-663. [Annotated scanned copy] %F A259866 a(n) = 3*10^A056807(n)+1. - _R. J. Mathar_, Jul 15 2015 %t A259866 Select[3*10^Range[70]+1,PrimeQ] (* _Harvey P. Dale_, Jul 05 2020 *) %Y A259866 Cf. A199683, A056807, A062339. %K A259866 nonn %O A259866 1,1 %A A259866 _N. J. A. Sloane_, Jul 08 2015