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 A235619 #13 Nov 02 2023 11:06:55 %S A235619 2,3,109,181,271,829,919,1549,1567,6661,6733,6823,8101,8191,8263, %T A235619 13933,14851,15319,22123,59149,59221,59239,59797,59887,61507,65629, %U A235619 65701,72253,72901,73819,118189,118927,119827,124669,125407,126127,126307,132679,132859 %N A235619 Primes whose base-9 representation also is the base-4 representation of a prime. %C A235619 This sequence is part of the two-dimensional array of sequences 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 A235619 Robert Price, <a href="/A235619/b235619.txt">Table of n, a(n) for n = 1..1296</a> %H A235619 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 A235619 E.g., 109 = 131_9 and 131_4 = 29 are both prime. %o A235619 (PARI) is(p,b=4,c=9)=vecmax(d=digits(p,c))<b&&isprime(vector(#d,i,b^(#d-i))*d~)&&isprime(p) %o A235619 (PARI) forprime(p=1,3e3,is(p,9,4)&&print1(vector(#d=digits(p,4),i,9^(#d-i))*d~,",")) \\ To produce the terms, this is more efficient than to select them using straightforwardly is(.)=is(.,4,9) %Y A235619 Cf. A235481, A235265, A235266, A152079, A235461 - A235482, A065720 - A065727, A235394, A235395, A089971 ⊂ A020449, A089981, A090707 - A091924, A235615 - A235639. See the LINK for further cross-references. %K A235619 nonn,base %O A235619 1,1 %A A235619 _M. F. Hasler_, Jan 13 2014