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 A141825 #3 Mar 31 2012 13:23:39 %S A141825 0,1,2,3,4,6,7,8,9,10,12,13,16,18,24,25,26,27,28,30,31,32,33,34,36,37, %T A141825 40,42,48,49,50,51,52,60,61,64,66,72,73,76,90,96 %N A141825 Encodes permutations which "avoid" the subsequence "123" based on the mapping described in A051683. %C A141825 Note that a(n) can be viewed as an irregular table with shape sequence 1 1 3 9 28 ... demonstrating the relationships with 1 2 5 14 42 ... Cf. A000108 and A000142. %C A141825 0 %C A141825 1 %C A141825 2 3 4 %C A141825 6 7 8 9 10 12 13 16 18 %C A141825 24 25 26 27 28 30 31 32 ... 96 %C A141825 120 ... %e A141825 The numbers 0 thru 4 map to 321,312,231,213 and 132 and are included because they avoid 123. The next number, 5, maps to 123 so is excluded from a(n). %Y A141825 Cf. A000108 A000142 A051683 A141824. %K A141825 more,nonn %O A141825 1,3 %A A141825 _Alford Arnold_, Jul 24 2008