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A015721
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Composite and even n such that phi(n) * sigma(n) is one less than a square.
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1
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6, 22, 44, 76, 82, 140, 190, 354, 392, 650, 944, 1072, 1142, 1150, 1668, 2276, 4176, 4192, 4262, 5090, 7260, 8660, 15026, 16064, 22926, 29746, 39436, 42872, 74666, 87498, 94786, 101882, 115772, 118928, 127580, 151348
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OFFSET
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1,1
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LINKS
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PROG
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(PARI) isok(n) = !isprime(n) && !(n%2) && issquare(eulerphi(n)*sigma(n)+1); \\ Michel Marcus, Oct 02 2017
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CROSSREFS
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Subsequence of even terms of A015709.
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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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