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 A057414 #14 Jun 24 2025 12:05:54 %S A057414 1,4,18,62,205,624,1841,5214,14448,39118,104281,273900,711416,1828950, %T A057414 4663203,11801056,29677044,74209404,184655403,457446252,1128794669, %U A057414 2775534900,6802886782,16625602146,40524317635 %N A057414 Number of staircase polygons of area n with one (staircase polygon) hole on square lattice (not allowing rotations). %H A057414 I. Jensen, <a href="/A057414/b057414.txt">Table of n, a(n) for n = 8..113</a> (from link below) %H A057414 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/polygons/series/staircase.area.1hole.ser">More terms</a> %K A057414 nonn %O A057414 8,2 %A A057414 _N. J. A. Sloane_, Aug 30 2000