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 A157644 #10 May 13 2013 01:54:10
%S A157644 9,18,28,37,41,45,46,56,65,75,84,88,92,93,97,107,116,126,135,139,143,
%T A157644 144,154,163,173,182,186,190,191,195,199,203,204,208,212,216,217,218,
%U A157644 219,229,238,248,257,261,265,266,276,285,295,304,308,312,313,317,327,336,346,355
%N A157644 Indices of 3's in A090822.
%C A157644 There is a group a(i+39) = a(i)+220 for i=1,..,39, then a group a(i+39)=a(i)+220 for i=40,...,78; these correlations become irregular later in the sequence.
%H A157644 Charles R Greathouse IV, <a href="/A157644/b157644.txt">Table of n, a(n) for n = 1..10000</a>
%t A157644 Clear[a]; reversed = {a[2] = 1, a[1] = 1}; blocs[len_] := Module[{bloc1, par, pos}, bloc1 = Take[reversed, len]; par = Partition[reversed, len]; pos = Position[par, bloc_ /; bloc != bloc1, 1, 1]; If[pos == {}, Length[par], pos[[1, 1]] - 1]]; a[n_] := a[n] = Module[{an}, an = Table[{blocs[len], len}, {len, 1, Quotient[n - 1, 2]}] // Sort // Last // First; PrependTo[reversed, an]; an]; Position[Table[a[n], {n, 1, 355}], 3] // Flatten (* _Jean-François Alcover_, Mar 25 2013 *)
%Y A157644 Cf. A157334, A107223, A157645.
%K A157644 nonn
%O A157644 1,1
%A A157644 _Paul Curtz_, Mar 03 2009
%E A157644 Extended by _R. J. Mathar_, Mar 15 2009