A264963 Number of down-up parking functions of length n.

1, 1, 1, 3, 17, 104, 915, 8618, 104436, 1337282, 20709209, 336013996, 6343919118, 124736306407, 2780356513594, 64249797198125, 1651884203936474, 43874277964032394, 1278413274487999471, 38372024627757454128, 1249821733374560346851, 41835183404896657899658

Offset

0,4

Links

Table of n, a(n) for n=0..21.

R. Stanley, Parking Functions, 2011

Formula

a(2n) = A260694(2n).

Example

a(3) = 3: 212, 213, 312.
a(4) = 17: 2121, 2131, 2132, 2141, 2142, 2143, 3121, 3131, 3132, 3141, 3142, 3231, 3241, 4121, 4131, 4132, 4231.
a(5) = 104: 21212, 21213, 21214, 21215, ..., 52314, 52412, 52413, 53412.

Crossrefs

Cf. A000111, A260694.

Sequence in context: A163064 A020069 A020024 * A036551 A162479 A194780

Adjacent sequences: A264960 A264961 A264962 * A264964 A264965 A264966

Keyword

nonn

Author

Alois P. Heinz, Nov 29 2015

Status

approved