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 A262649 #7 Oct 31 2015 15:02:41 %S A262649 2,525,1252521,512525215,102512525215201,5110251252521520115, %T A262649 151102512525215201151,5515110251252521520115155, %U A262649 50551511025125252152011515505,525055151102512525215201151550525,1152505515110251252521520115155052511 %N A262649 Minimal nested palindromic base-6 primes with seed 2; see Comments. %C A262649 Using only base-6 digits 0,1,2,3,4,5, let s be a palindrome and put a(1) = s. Let a(2) be the least palindromic prime having s in the middle; for n > 2, let a(n) be the least palindromic prime have a(n-1) in the middle. Then (a(n)) is the sequence of minimal nested palindromic base-6 primes with seed s. %H A262649 Clark Kimberling, <a href="/A262649/b262649.txt">Table of n, a(n) for n = 1..300</a> %e A262649 a(3) = 1252521 is the least base-6 prime having a(2) = 525 in its middle. Triangular format: %e A262649 2 %e A262649 525 %e A262649 1252521 %e A262649 512525215 %e A262649 102512525215201 %e A262649 5110251252521520115 %t A262649 s = {2}; base = 6; z = 20; Do[NestWhile[# + 1 &, 1, ! PrimeQ[tmp = FromDigits[Join[#, IntegerDigits[Last[s]], Reverse[#]] &[IntegerDigits[#, base]], base]] &]; %t A262649 AppendTo[s, FromDigits[IntegerDigits[tmp, base]]], {z}]; s (* A262649 *) %t A262649 Map[FromDigits[ToString[#], base] &, s] (* A262650 *) %t A262649 (* _Peter J. C. Moses_, Sep 01 2015 *) %Y A262649 Cf. A261881 (base 10), A262650, A262627. %K A262649 nonn,easy,base %O A262649 1,1 %A A262649 _Clark Kimberling_, Oct 27 2015