login
A264963
Number of down-up parking functions of length n.
1
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
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
Sequence in context: A163064 A020069 A020024 * A036551 A162479 A194780
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 29 2015
STATUS
approved