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A034806
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Number of unique sets of 2 numbers > 1 such that their product is between n^2 and (n+1)^2.
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2
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2, 5, 9, 12, 17, 22, 28, 32, 40, 41, 50, 56, 63, 68, 78, 80, 91, 94, 102, 110, 120, 123, 131, 141, 148, 156, 166, 163, 179, 185, 195, 206, 214, 211, 229, 237, 248, 248, 265, 260, 281, 284, 296, 305, 314, 320, 333, 337
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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FORMULA
| sum(floor( (2n+(n^2)%k)/k), for k=2..n).
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EXAMPLE
| a(3)=5 because the only pairs of numbers > 1 that form a product between 3^2 and 4^2 are (2,5) (2,6) (3,4) (2,7) (3,5).
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PROG
| (PARI) A034806(n) = sum(k=2, n, floor(((n+1)^2-1)/k)-floor(n^2/k)) [From Michael B. Porter (michael_b_porter(AT)yahoo.com), Mar 13 2010]
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CROSSREFS
| Cf. A037048, A037092.
Sequence in context: A086814 A086343 A056549 * A034307 A070828 A112988
Adjacent sequences: A034803 A034804 A034805 * A034807 A034808 A034809
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KEYWORD
| nonn
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AUTHOR
| Joe K. Crump (joecr(AT)carolina.rr.com)
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