A141825 - OEIS

A141825

Encodes permutations which "avoid" the subsequence "123" based on the mapping described in A051683.

%I #3 Mar 31 2012 13:23:39

%S 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 40,42,48,49,50,51,52,60,61,64,66,72,73,76,90,96

%N Encodes permutations which "avoid" the subsequence "123" based on the mapping described in A051683.

%C 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 0

%C 1

%C 2 3 4

%C 6 7 8 9 10 12 13 16 18

%C 24 25 26 27 28 30 31 32 ... 96

%C 120 ...

%e 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 Cf. A000108 A000142 A051683 A141824.

%K more,nonn

%O 1,3

%A _Alford Arnold_, Jul 24 2008