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A019507
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Droll numbers: sum of even prime divisors equals sum of odd prime divisors.
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9
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72, 240, 672, 800, 2240, 4224, 5184, 6272, 9984, 14080, 17280, 33280, 39424, 48384, 52224, 57600, 93184, 116736, 161280, 174080, 192000, 247808, 304128, 373248, 389120, 451584, 487424, 537600, 565248, 585728, 640000, 718848
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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6272 = 2*2*2*2*2*2*2*7*7 is droll since 2+2+2+2+2+2+2 = 14 = 7+7.
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PROG
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(PARI) isok(n) = {if (n % 2, return (0)); f = factor(n); return (2*f[1, 2] == sum(i=2, #f~, f[i, 1]*f[i, 2])); } \\ Michel Marcus, Jun 21 2013
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CROSSREFS
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For count instead of sum we have A072978.
Partitions of this type are counted by A239261, without zero terms A249914.
For prime indices instead of factors we have A366748, zeros of A366749.
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KEYWORD
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nonn
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AUTHOR
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Mario Velucchi (mathchess(AT)velucchi.it)
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STATUS
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approved
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