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 A234813 #14 Apr 22 2014 09:56:21 %S A234813 1,3,5,9,12,16,21,27,33,40,47,55,63,70,77,89,101,110,123,134,146,159, %T A234813 171,186,200,214,229,245,260,275,293,312,329,349,369,388,411,432,451, %U A234813 474,496,519,542,564,586,611,635,660,689,713 %N A234813 Number of distinct integers of the form i+(i+1)+(i+2)+...+j, for 1 <= i <= j <= n. %C A234813 See also A001227 = number of ways to write n as difference of triangular numbers. - _M. F. Hasler_, Apr 20 2014 %e A234813 a(3) = 5 because the possible integers are 1,2,3=1+2,5=2+3,6=1+2+3. %K A234813 nonn %O A234813 1,2 %A A234813 _Jeffrey Shallit_, Apr 19 2014