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 A239203 #9 Jan 12 2016 16:22:13 %S A239203 0,11,218987,55844736,8299697699240,2585386023324464 %N A239203 Numbers k such that k+x+y is a square and k+u+v is a triangular number, where x and y are the two squares nearest to k, while u and v are the two triangular numbers nearest to k. %C A239203 Intersection of A239071 and A238489. %e A239203 11 is in the sequence because the two squares nearest to 11 are 9 and 16 and 11+9+16=36 is a square, and also the two triangular numbers nearest to 11 are 10 and 15, and 11+10+15=36 is a triangular number. %e A239203 Similarly, 218987 is in the sequence because 218987+467^2+468^2=656100 is a square, and 218987+triangular(661)+triangular(662)=657231 is a triangular number. %Y A239203 Cf. A000217, A000290, A238489, A239071. %K A239203 nonn,hard,more %O A239203 1,2 %A A239203 _Alex Ratushnyak_, Mar 12 2014 %E A239203 a(5)-a(6) from _Lars Blomberg_, Jan 12 2016