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 A231481 #21 Jan 17 2022 00:28:02 %S A231481 2,3,5,13,17,29,59,67,71,73,97,127,191,199,223,227,239,307,337,349, %T A231481 353,367,409,421,433,449,461,479,487,491,563,571,577,619,647,683,739, %U A231481 743,811,823,829,857,881,911,937,941,991,1021,1051,1091,1103,1117,1163,1201,1217,1259,1277,1289 %N A231481 Primes whose base-6 representation is also the base-9 representation of a prime. %C A231481 This sequence is part of a two-dimensional array of sequences, given in the LINK, based on this same idea for any two different bases b, c > 1. Sequence A235265 and A235266 are the most elementary ones in this list. Sequences A089971, A089981 and A090707 through A090721, and sequences A065720 - A065727, follow the same idea with one base equal to 10. %H A231481 Giovanni Resta, <a href="/A231481/b231481.txt">Table of n, a(n) for n = 1..10000</a> %H A231481 M. F. Hasler, <a href="https://docs.google.com/document/d/10IM7fcAbB2tqRGuwfGvuEGUzD_IXbgXPDK0tfxN4M3o/pub">Primes whose base c expansion is also the base b expansion of a prime</a> %e A231481 13 = 21_6 and 21_9 = 19 are both prime, so 13 is a term. %t A231481 Select[Prime[Range[300]],PrimeQ[FromDigits[IntegerDigits[#,6],9]]&] (* _Harvey P. Dale_, Aug 30 2015 *) %o A231481 (PARI) is(p,b=9,c=6)=isprime(vector(#d=digits(p,c),i,b^(#d-i))*d~)&&isprime(p) \\ Note: This code is only valid for b > c. %Y A231481 Cf. A235639, A235265, A235266, A152079, A235461 - A235482, A065720 - A065727, A235394, A235395, A089971 ⊂ A020449, A089981, A090707 - A091924, A235615 - A235639. See the LINK for further cross-references. %K A231481 nonn,base %O A231481 1,1 %A A231481 _M. F. Hasler_, Jan 13 2014