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 A257471 #19 May 08 2015 18:20:58
%S A257471 1,2,3,4,6,5,8,9,10,12,7,15,16,14,18,20,21,24,25,28,30,11,27,32,35,36,
%T A257471 22,40,42,13,33,45,48,49,26,44,50,54,56,39,55,60,63,64,52,66,70,72,17,
%U A257471 65,77,80,81,34,78,84,88,90,19,51,75,91,96,99,100
%N A257471 Sequence obtained from A003991 (multiplication table read by antidiagonals) by removing repetitions.
%C A257471 A permutation of positive integers.
%H A257471 Ivan Neretin, <a href="/A257471/b257471.txt">Table of n, a(n) for n = 1..10000</a>
%H A257471 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%e A257471 The infinite multiplication table
%e A257471 1...2...3...4...5...
%e A257471 2...4...6...8..10...
%e A257471 3...6...9..12..15...
%e A257471 4...8..12..16..20...
%e A257471 5..10..15..20..25...
%e A257471 ...
%e A257471 reads by antidiagonals as follows: 1, 2, 2, 3, 4, 3, 4, 6, 6, 4, 5, 8, 9, 8, 5, ... (A003991). By removing all numbers that were encountered previously, we get 1, 2, 3, 4, 6, 5, 8, 9, ...
%t A257471 DeleteDuplicates[Flatten[Table[i * (n - i), {n, 20}, {i, n - 1}]]]
%Y A257471 Cf. A003991 (multiplication table), A257472 (inverse permutation).
%K A257471 nonn,easy,look
%O A257471 1,2
%A A257471 _Ivan Neretin_, Apr 25 2015