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 A215637 #24 Feb 01 2015 09:31:58
%S A215637 1,1,1,2,7,72,2144,2641,1345721,2191254096
%N A215637 Number of solutions of square array of integers, choosing one prime from each row and column.
%C A215637 Let p be the n-th prime number. Put 1 to p^2 into a square array in order. Choose a set of primes such that there is one and only one in each row and column. This is equivalent to non-attacking rooks on prime-numbered squares. Then a(n) is the number of solutions for the n-th prime.
%D A215637 Martin Erickson, Beautiful Mathematics, Mathematical Association of America, 2011, p. 6. The problem is called Transversal of primes.
%H A215637 J. K. Andersen, W. Edwin Clark, Jud McCranie, Carlos Rivera, Emmanuel Vantieghem, <a href="http://www.primepuzzles.net/puzzles/puzz_649.htm">Puzzle 649</a> (www.primepuzzles.net)
%e A215637 For n=2, p=3, and the only solution is {3,5,7}, so a(2) = 1.
%Y A215637 Cf. A000217, A000040.
%K A215637 nonn,more,hard
%O A215637 1,4
%A A215637 _Jud McCranie_, Aug 18 2012