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 A138553 #14 Jun 19 2014 04:50:53
%S A138553 1,1,2,1,2,2,2,1,3,1,2,2,3,1,3,1,3,2,2,1,4,1,2,2,3,2,3,1,3,2,3,1,4,1,
%T A138553 2,3,3,1,3,1,4,2,2,1,4,2,2,2,3,1,4,1,3,2,2,2,4,1,2,2,4,1,3,1,3,3,2,1,
%U A138553 4,1,3,2,3,1,3,2,3,2,2,1,5,1,2,2,3,2,4,1,3,2,3,1,5,1,2,3,3,1,4,1,4,2,2,1,5
%N A138553 Table read by rows: T(n,k) is the number of divisors of k that are <= n.
%C A138553 Suggested by a question from _Eric Desbiaux_.
%C A138553 The row lengths are the lengths before the pattern for n repeats.
%C A138553 Antidiagonal sums A070824. [From _Eric Desbiaux_, Dec 10 2009]
%F A138553 T(n,k) = sum_{i|k, i<=n} 1.
%e A138553 The first few rows start:
%e A138553 1, [A000012]
%e A138553 1, 2, [A000034]
%e A138553 1, 2, 2, 2, 1, 3, [A083039]
%e A138553 1, 2, 2, 3, 1, 3, 1, 3, 2, 2, 1, 4, [A083040]
%o A138553 (PARI) lista(nrows) = {for (n=1, nrows, for (k=1, lcm(vector(n, i, i)), print1(sumdiv(k, d, d <=n), ", ");); print(););} \\ _Michel Marcus_, Jun 19 2014
%Y A138553 Row lengths A003418, row sums A025529, frequencies in rows A096180.
%Y A138553 Cf. A243987
%K A138553 easy,nonn,tabf
%O A138553 1,3
%A A138553 _Franklin T. Adams-Watters_, Mar 24 2008
%E A138553 Definition corrected by _Franklin T. Adams-Watters_, Jun 19 2014