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A079486 Number of different solutions to a variant of the 3-ball tennis ball problem. 2
3, 15, 103, 879, 8787, 99061, 1227369, 16409937, 233588249, 3504149013, 54963273921, 895797910129 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

You're given labeled balls three at time (labeled 1,2,3 then 4,5,6 etc.), choose two balls from those still on hand (including the three you've just been given) and throw the larger out the window onto the front lawn, the smaller onto the back lawn.

REFERENCES

Larger numbers computed by Matt Richey.

LINKS

Table of n, a(n) for n=1..12.

FORMULA

a(n) is the number of 2 X n matrices of positive integers, with the numbers in each row and column increasing, the numbers in column k less than or equal to 3k and no number used more than once.

CROSSREFS

Cf. A000108, A001764, A002293, A049235.

Sequence in context: A174493 A318618 A123184 * A245118 A331689 A001274

Adjacent sequences:  A079483 A079484 A079485 * A079487 A079488 A079489

KEYWORD

nonn

AUTHOR

Barry Cipra, Jan 19 2003

STATUS

approved

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Last modified July 9 16:50 EDT 2020. Contains 335545 sequences. (Running on oeis4.)