A230555 Number of involutions avoiding 3421.

1, 1, 2, 4, 10, 25, 66, 173, 460, 1218, 3240, 8602, 22878, 60794, 161668, 429752, 1142758, 3038173, 8078606, 21479469, 57113888

Offset

0,3

Links

Table of n, a(n) for n=0..20.

Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, Pattern-avoiding involutions: exact and asymptotic enumeration, arxiv:1310.7003, 2013.

Example

Of the 26 involutions of length 5, only 45312 contains the pattern 3421, so a(5) = 25.

Crossrefs

Cf. A000085, A001006, A121704, A230551-A230556.

Sequence in context: A005958 A166516 A230552 * A189912 A268321 A195981

Adjacent sequences: A230552 A230553 A230554 * A230556 A230557 A230558

Keyword

nonn

Author

Cheyne Homberger, Oct 23 2013

Status

approved