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 A381256 #12 Mar 08 2025 20:22:57 %S A381256 0,1,625,57057,7748433,30850281,111494625,393423745,499088601, %T A381256 519341361,1051107705,1329416385,1616038425,2215448001,2433936225, %U A381256 2852972265,3399207273,4344683849,4961725281,5454760185,5485530369,6578054145,6678031745,7701979761,7807302825 %N A381256 Numbers k such that 5*k+1 divides 5^k+1. %C A381256 The numbers are called Curzon numbers by Tattersall (p. 85, exercise 43). %D A381256 James J. Tattersall, Elementary Number Theory in Nine Chapters, Second Edition, Cambridge University Press, 2005, p. 85. %H A381256 Giovanni Resta, <a href="https://www.numbersaplenty.com/set/Curzon_number/">Curzon numbers</a>, Numbers Aplenty. %e A381256 5*625+1 = 3126 divides 5^625+1. %o A381256 (PARI) isok(n) = my(m=5*n+1); Mod(5, m)^n==-1 %Y A381256 Cf. A224486, A222948, A230076, A381257, A381258. %K A381256 nonn %O A381256 1,3 %A A381256 _René-Louis Clerc_, Feb 18 2025