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 A091730 #6 Aug 20 2015 03:00:40 %S A091730 4,5,6,9,14,21,29,41,46,49,61,69,86,89,94,101,109,121,129,134,141,149, %T A091730 161,166,169,181,201,206,214,229,241,249,254,269,281,289,301,309,321, %U A091730 326,329,334,349,361,381,389,401,409,421,446,449,454,461,469,489 %N A091730 Norms of irreducible elements of Z[sqrt(-5)]. %C A091730 The following lists the types of numbers which appear (p,q are distinct primes, congruences are mod 20 and the number in square brackets gives the number of irreducible elements of that norm counting a and -a only once): 4 [1]; 5 [1]; p==1,9 [2]; p^2 where p==-1,-3,-7,-9 [1]; 2p where p==3,7 [2]; p^2 where p==3,7 [3]; pq where p,q==3,7 [4]. %D A091730 David A. Cox, Primes of the form x^2+ny^2, Wiley, 1989. %D A091730 A. Frohlich and M. J. Taylor, Algebraic number theory, Cambridge university press, 1991. %K A091730 easy,nonn %O A091730 0,1 %A A091730 _Paul Boddington_, Feb 02 2004