A141825 Encodes permutations which "avoid" the subsequence "123" based on the mapping described in A051683.

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

Offset

1,3

Comments

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.

0

1

2 3 4

6 7 8 9 10 12 13 16 18

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

120 ...

Links

Table of n, a(n) for n=1..42.

Example

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).

Crossrefs

Cf. A000108 A000142 A051683 A141824.

Sequence in context: A260816 A285598 A275804 * A238369 A296858 A296241

Adjacent sequences: A141822 A141823 A141824 * A141826 A141827 A141828

Keyword

more,nonn

Author

Alford Arnold, Jul 24 2008

Status

approved