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 A138275 #2 Mar 30 2012 18:37:09 %S A138275 1,2,18,268,5320,129474,3700550,121016160,4448701704,181463572394, %T A138275 8130511993010,396880976034092,20963000461338000,1191187898025406514, %U A138275 72455444438093714542,4697146562744837487104,323299667265950287087968 %N A138275 Central terms of triangle A138271. %Y A138275 Cf. A138271; A138272, A138273, A138274. %K A138275 nonn %O A138275 0,2 %A A138275 _Paul D. Hanna_, Mar 11 2008