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Search: id:A120253
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| A120253 |
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Number of subsets of integers in the interval [n^2+1, (n+1)^2-1] whose product is twice a square. |
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3
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| 1, 1, 1, 1, 2, 1, 2, 4, 2, 4, 4, 4, 8, 4, 32, 8, 16, 16, 32, 16, 32, 128, 32, 64, 64, 128, 512, 32, 512, 128, 256, 2048, 256, 2048, 256, 1024, 512, 8192, 4096, 1024, 4096, 4096, 8192, 16384, 4096, 32768, 32768, 4096, 131072, 16384, 131072, 16384, 524288
(list; graph; listen)
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OFFSET
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1,5
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COMMENT
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Also the number of subsets in the same interval whose product is precisely a square, if 1 is included.
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LINKS
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Andrew Granville and John Selfridge, Product of integers in an interval, modulo squares (pdf), Electronic Journal of Combinatorics, Volume 8(1), 2001.
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FORMULA
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2^A120254(n)
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EXAMPLE
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a(5) = 2 because the interval [26,35] contains two sets of such integers: {32} and {27,28,30,35}.
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CROSSREFS
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Cf. A120254. A099500 is the number of distinct products which are twice a square. A099501 is the smallest size of a subset which is twice a square.
Sequence in context: A099254 A121339 A099500 this_sequence A060547 A079878 A137406
Adjacent sequences: A120250 A120251 A120252 this_sequence A120254 A120255 A120256
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KEYWORD
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nonn
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AUTHOR
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Martin Fuller (martin_n_fuller(AT)btinternet.com), Jun 13 2006
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