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 A047818 #10 Mar 07 2020 00:39:18 %S A047818 1,1,2,1,5,1,2,10,2,10,13,5,1,10,2,10,13,5,37,2,34,1,50,34,17,1,25,13, %T A047818 10,65,2,41,65,53,5,29,34,10,1,50,2,74,10,26,5,85,106,5,25,13,1,10,26, %U A047818 2,61,37,34,17,5,1,26,13,170,10,2,5,130,58,125,106,73,130,50,26,170 %N A047818 a(n) is the least number m such that A002313(n)*m - 1 is a square. %C A047818 A002313 has the 4k+1 and 4k+2 primes. %C A047818 Related to Stormer numbers. %H A047818 J. Todd, <a href="https://www.jstor.org/stable/2305526">A problem on arc tangent relations</a>, Amer. Math. Monthly, 56 (1949), 517-528. %F A047818 a(n) = ((A002314(n-1))^2 + 1) / A002313(n). %e A047818 a(3) = 2 because A002313(3)=13 and 13*2-1 = 5^2. %Y A047818 Cf. A002313, A002314, A005528. %K A047818 nonn %O A047818 1,3 %A A047818 _N. J. A. Sloane_ %E A047818 Edited by _Don Reble_, Apr 13 2006