A269121 Number of sequences with n copies each of 1,2,3 avoiding the pattern 123.

1, 5, 43, 374, 3199, 26945, 224296, 1850672, 15168751, 123700631, 1004849563, 8137906034, 65749071892, 530209766156, 4269268590280, 34334967161024, 275866609658095, 2214734413345667, 17769222356447761, 142492124882039978, 1142168892887289319

Offset: 0

Author

Alois P. Heinz, Feb 19 2016

Keywords

• nonn

Examples

			a(0) = 1: the empty sequence.
a(1) = 5: 132, 213, 231, 312, 321.
a(2) = 43: 113322, 131322, 133122, 133212, 133221, 211332, 213132, 213312, 213321, 221133, 221313, 221331, 223113, 223131, 223311, 231132, 231312, 231321, 232113, 232131, 232311, 233112, 233121, 233211, 311322, 313122, 313212, 313221, 321132, 321312, 321321, 322113, 322131, 322311, 323112, 323121, 323211, 331122, 331212, 331221, 332112, 332121, 332211.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..1000

Crossrefs

Row n=3 of A269129.

Cf. A006480, A047911.

Formula

a(n) = A006480(n) - A047911(n).