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 A056138 #11 Dec 11 2019 22:05:38 %S A056138 0,0,1,0,1,1,1,1,2,1,1,2,1,1,3,2,1,2,1,3,3,1,1,4,2,1,3,3,1,3,1,3,4,1, %T A056138 3,5,1,1,4,5,1,3,1,3,5,1,1,7,2,2,4,3,1,3,3,5,4,1,1,9,1,1,5,4,4,4,1,3, %U A056138 4,3,1 %N A056138 Number of ways in which n can be the shorter leg (shortest side) of an integer-sided right triangle. %F A056138 a(n) = A046079(n) - A056137(n) = A046081(n) - A046080(n) - A056137(n). %o A056138 (PARI) a(n)=my(b);sum(c=n+2,n^2\2+1,issquare(c^2-n^2,&b) && n<b) \\ _Charles R Greathouse IV_, Jul 07 2013 %Y A056138 Cf. A009004, A055525, A055527. %K A056138 nonn %O A056138 1,9 %A A056138 _Henry Bottomley_, Jun 15 2000