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 A034276 #24 May 18 2020 06:36:52
%S A034276 11,29,2,5,41,251,43,145577,51941,4372877,26901631,366636187,
%T A034276 15387286403,218761753811,3313980408469
%N A034276 Smallest prime that generates a prime pyramid of height n.
%C A034276 Let p be prime; look for the smallest prime in {1|p|1, 3|p|3, 7|p|7, 9|p|9}, where '|' stands for concatenation; repeat until no such prime can be found; then height(p) = number of rows in pyramid.
%C A034276 a(13) > 10^10. - _Donovan Johnson_, Aug 13 2010
%H A034276 H. Heinz, Patterns in Primes, <a href="http://www.magic-squares.net/primes.htm">Illustrating Two Prime Pyramids</a>
%H A034276 Chai Wah Wu, <a href="http://arxiv.org/abs/1503.08883">On a conjecture regarding primality of numbers constructed from prepending and appending identical digits</a>, arXiv:1503.08883 [math.NT], 2015.
%e A034276 Example for p=43: 43 3433 334333 93343339 3933433393 939334333939 39393343339393, stop; height(43)=7.
%Y A034276 Cf. A047076, A053600, A052205, A256957, A052091, A052092.
%K A034276 nonn,nice,base,more
%O A034276 1,1
%A A034276 _Felice Russo_, Jan 25 2000
%E A034276 More terms from _Naohiro Nomoto_, Jul 14 2001
%E A034276 a(11)-a(12) from _Donovan Johnson_, Aug 13 2010
%E A034276 a(13) from _Chai Wah Wu_, Apr 10 2015
%E A034276 a(14)-a(15) from _Giovanni Resta_, May 15 2020