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 A383907 #16 May 20 2025 18:40:55 %S A383907 13,73,127,163,193,197,313,337,419,433,757,929,1153,2017,2311,2593, %T A383907 2647,3137,3659,4483,4673,5741,6857,7057,12071,12097,13267,13313, %U A383907 13619,14407,15877,17191,18041,18433,18439,19273,19531,20353,21319,21961,22279,24103,24697,25411 %N A383907 Echo primes: primes p such that the greatest prime factor of p-1 is a suffix of p. %C A383907 These are primes in A383896(n). %C A383907 The first pair of twin echo primes is 6467806769 and 6467806771. %C A383907 Conjecture: There are infinitely many echo primes. %t A383907 Select[Prime@Range@3000,(f=FactorInteger[#-1][[-1,1]]; Mod[#,10^IntegerLength@f]==f)&] %o A383907 (Python) %o A383907 from sympy import factorint, isprime %o A383907 def ok(n): return n > 2 and isprime(n) and str(n).endswith(str(max(factorint(n-1)))) %o A383907 print([k for k in range(30000) if ok(k)]) # _Michael S. Branicky_, May 15 2025 %Y A383907 Cf. A000040, A006530, A383896. %K A383907 nonn,base %O A383907 1,1 %A A383907 _Giorgos Kalogeropoulos_, May 15 2025