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A181794
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Numbers n such that the number of even divisors of n is an even divisor of n.
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3
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4, 6, 10, 12, 14, 16, 20, 22, 24, 26, 28, 34, 36, 38, 44, 46, 48, 52, 58, 62, 68, 74, 76, 80, 82, 86, 90, 92, 94, 106, 112, 116, 118, 120, 122, 124, 126, 134, 142, 144, 146, 148, 150, 158, 160, 164, 166, 168, 172, 176, 178, 180, 188, 192, 194, 198, 202, 206, 208, 212, 214, 216, 218, 226, 234, 236, 240, 244, 252, 254, 256, 262, 264, 268, 272, 274, 278
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OFFSET
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1,1
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COMMENTS
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All terms are even, since odd numbers, even if they have an even count of divisors, don't have any even divisors.
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LINKS
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EXAMPLE
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a(4)=12 has four even divisors (2, 4, 6, and 12), and 4 is one of those even divisors.
The number 21 is not in this sequence: it has four divisors (1, 3, 7, and 21), and 4 is not one of those divisors.
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MATHEMATICA
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Select[Range[2, 1000, 2], EvenQ[DivisorSigma[0, #/2]] && MemberQ[Divisors[#], DivisorSigma[0, #/2]] &]
Select[Range[2, 278, 2], EvenQ[(d = DivisorSigma[0, #/2])] && Divisible[#, d] &] (* Amiram Eldar, Aug 29 2019 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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