A214611 Number of permutations of length n sortable by a pop stack followed by a queue and then by a stack.

1, 2, 6, 24, 120, 685, 4148, 25661, 159829, 997870, 6240672, 39111747, 245782289, 1549368610

Offset: 1

Author

Vincent Vatter, Mar 06 2013

Keywords

• nonn
• hard
• more

Examples

			There are only a(6)=685 permutations of length 6 that can be sorted by this machine; the machine can sort all shorter permutations.
		

Links

• R. Smith and V. Vatter, A stack and a pop stack in series, The Australasian Journal of Combinatorics, Volume 58(1) (2014), pp. 157-171.

Crossrefs

Cf. A033321.

Extensions

a(11)-a(14) from Bert Dobbelaere, Jun 18 2024