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A079486
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Number of different solutions to a variant of the 3-ball tennis ball problem.
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2
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3, 15, 103, 879, 8787, 99061, 1227369, 16409937, 233588249, 3504149013, 54963273921, 895797910129
(list;
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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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.
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REFERENCES
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Larger numbers computed by Matt Richey.
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LINKS
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Table of n, a(n) for n=1..12.
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FORMULA
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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.
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CROSSREFS
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Cf. A000108, A001764, A002293, A049235.
Sequence in context: A185753 A174493 A123184 * A001274 A139766 A003276
Adjacent sequences: A079483 A079484 A079485 * A079487 A079488 A079489
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KEYWORD
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nonn
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AUTHOR
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Barry Cipra, Jan 19 2003
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STATUS
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approved
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