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A071008
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Numbers n such that uphi(uphi(n)) = n/2.
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1
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2, 4, 16, 256, 364, 1456, 3276, 13104, 21600, 23296, 65536, 209664, 249984, 367200, 1285632, 3110400, 5963776, 6596304, 9749376, 23046144, 27216000, 33022080, 52876800, 53673984, 76639680, 94370400, 105540864, 119992320, 245765520, 285405120, 426037248
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OFFSET
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1,1
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COMMENTS
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If n = Product p_i^r_i then uphi(n) = Product (p_i^r_i-1); for example uphi(12) = (4-1)*(3-1) = 6.
If 2^n+1 is a Fermat prime then 2^(2*n) is a solution of the equation.
3110400 and 4294967296 are also in the sequence.
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LINKS
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FORMULA
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PROG
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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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