A171074 A115112 with initial term changed from 0 to 1.

1, 4, 18, 68, 250, 922, 3430, 12868, 48618, 184754, 705430, 2704154, 10400598, 40116598, 155117518, 601080388, 2333606218, 9075135298, 35345263798, 137846528818, 538257874438, 2104098963718, 8233430727598, 32247603683098

Offset

1,2

Comments

From a variant of the tennis ball problem (cf. A031970, A049235). On turn n ball 2n-1 is introduced to the room, ball 2n is introduced to the garden, then one of the balls in the room is swapped with one of the balls in the garden. The present sequence gives the number of combinations, while A171075 gives the total on the lawn, A170076 gives the total in the room.

References

David Scambler, Just for fun, more tennis balls, Posting to the Sequence Fans Mailing List, Aug 25 2010.

Links

Table of n, a(n) for n=1..24.

Crossrefs

Cf. A031970, A049235, A171075, A171076.

Sequence in context: A231950 A246134 A115112 * A005367 A050184 A263582

Adjacent sequences: A171071 A171072 A171073 * A171075 A171076 A171077

Keyword

nonn

Author

N. J. A. Sloane, Sep 06 2010

Status

approved