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A166602
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Numbers k such that Sum_{i=1..k} i^2 divides Product_{i=1..k} i^2.
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7
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1, 7, 13, 17, 19, 24, 25, 27, 31, 32, 34, 37, 38, 43, 45, 47, 49, 55, 57, 59, 61, 62, 64, 67, 71, 73, 76, 77, 79, 80, 84, 85, 87, 91, 92, 93, 94, 97, 101, 103, 104, 107, 109, 110, 115, 117, 118, 121, 122, 123, 124, 127, 129, 132, 133, 137, 139, 142, 143, 144, 145, 147
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OFFSET
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1,2
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COMMENTS
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Product_{i=1..k} i^2 = (k!)^2 and Sum_{i=1..k} i^2 = k(k-1)(2k-1)/6 [From J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010]
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LINKS
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J. Mulder, Table of n, a(n) for a(n) below 20000
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EXAMPLE
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a(2) = A125314(2) = 7.
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MATHEMATICA
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Cases[Range[2, 5000], k_ /; Divisible[Factorial[k - 1]^2, 1/6 (-1 + k) k (-1 + 2 k)]] - 1 [From J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010]
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CROSSREFS
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Cf. A125314, A060462, A166604, A166605, A166606, A166607, A166608, A166609, A166610.
Cf. A067656. [From R. J. Mathar, Oct 23 2009]
Sequence in context: A144426 A118942 A067656 * A079697 A079695 A079698
Adjacent sequences: A166599 A166600 A166601 * A166603 A166604 A166605
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KEYWORD
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nonn
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AUTHOR
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Alexander Adamchuk, Oct 18 2009
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EXTENSIONS
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Terms below 5000 - J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010
More terms copied from the b-file - R. J. Mathar, Feb 14 2010
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STATUS
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approved
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