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 A235474 #15 Jan 16 2022 23:30:39 %S A235474 2,3,11,29,31,41,101,109,139,149,151,181,199,229,239,251,269,271,281, %T A235474 389,409,491,509,541,547,661,751,887,911,947,991,1021,1051,1061,1069, %U A235474 1091,1151,1279,1289,1381,1409,1471,1549,1709,1759,1801,1999 %N A235474 Primes whose base-4 representation is also the base-5 representation of a prime. %C A235474 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. %C A235474 For further motivation and cross-references, see sequence A235265 which is the main entry for this whole family of sequences. %H A235474 Harvey P. Dale, <a href="/A235474/b235474.txt">Table of n, a(n) for n = 1..1000</a> %H A235474 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 A235474 11 = 23_4 and 23_5 = 13 are both prime, so 11 is a term. %t A235474 Select[Prime[Range[400]],PrimeQ[FromDigits[IntegerDigits[#,4],5]]&] (* _Harvey P. Dale_, Dec 31 2017 *) %o A235474 (PARI) is(p,b=5,c=4)=isprime(vector(#d=digits(p,c),i,b^(#d-i))*d~)&&isprime(p) \\ Note: This code is only valid for b > c. %Y A235474 Cf. A235266, A235473, A152079, A235475 - A235479, A065720 ⊂ A036952, A065721 - A065727, A235394, A235395, A089971 ⊂ A020449, A089981, A090707 - A091924, A235461 - A235482. See the LINK for further cross-references. %K A235474 nonn,base %O A235474 1,1 %A A235474 _M. F. Hasler_, Jan 12 2014