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 A172294 #7 Oct 05 2019 16:34:39 %S A172294 12,42,1152,1452,1950,3672,5520,6660,8232,10890,13218,15288,15360, %T A172294 16062,18042,20898,21018,23562,23628,25998,27918,32190,37812,42018, %U A172294 42462,48858,55818,57192,80832,80910,83232,83340,91368,97848,98640 %N A172294 Sequence of the "Natural Jewels": a natural jewel is a number that is totally enclosed by prime numbers in a version of Ulam Spiral. %C A172294 There is no formula to calculate these numbers. If the sequence is infinite, then there are infinitely many primes p such that p + 2 is also prime (twin prime conjecture). %H A172294 Emilio Apricena, <a href="/A172294/a172294.png">Illustration</a> %e A172294 11-(top)->12, 13-(left)->12, 29-(right)->12, 31-(bottom)->12. %Y A172294 Cf. A156859. %K A172294 nonn %O A172294 1,1 %A A172294 Emilio Apricena (emilioapricena(AT)yahoo.it), Jan 30 2010 %E A172294 Corrected and extended by Emilio Apricena (emilioapricena(AT)yahoo.it), May 15 2010