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 A240168 #13 Aug 05 2014 14:13:44 %S A240168 0,1,1,1,1,2,2,1,1,2,3,5,4,2,1,1,2,4,8,13,15,16,11,5,2,1,1,2,4,9,19, %T A240168 35,55,75,83,72,51,29,13,5,2,1,1,2,4,10,22,50,105,196,338,511,649,695, %U A240168 627,473,304,172,83,35,14,5,2,1 %N A240168 T(n,k) is the number of unlabeled graphs of n vertices and k edges that have endpoints, where an endpoint is a vertex with degree 1. %C A240168 The length of the rows are 1,1,2,4,7,11,16,22,...: (n-1)*(n-2)/2 + 1 = A152947(n). %C A240168 T(n,k) = 0 if k > (n-1)*(n-2)/2 + 1. (Cf. A245796) %e A240168 First few rows of irregular triangle are: %e A240168 ..0 %e A240168 ..1 %e A240168 ..1....1 %e A240168 ..1....2....2....1 %e A240168 ..1....2....3....5....4....2....1 %e A240168 ..1....2....4....8...13...15...16...11....5....2....1 %e A240168 ..1....2....4....9...19...35...55...75...83...72...51...29...13....5....2....1 %e A240168 ... %Y A240168 Cf. A245796. Sum of n-th row is equal to A141580(n). %K A240168 nonn,tabf %O A240168 1,6 %A A240168 _Chai Wah Wu_, Aug 02 2014