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A067242
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Numbers m such that sigma(m+1)+sigma(m-1) = 5*phi(m).
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1
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2, 3, 4, 32, 58, 133, 221, 377, 407, 472, 1241, 1978, 7232, 13181, 13952, 15323, 15409, 17362, 22328, 32048, 44215, 46192, 46498, 46975, 49228, 73169, 74498, 128723, 177305, 241828, 244352, 297477, 306835, 417728, 450023, 455555, 484942, 640729, 693259, 707881, 803509
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Select[Range[804000], DivisorSigma[1, #+1]+DivisorSigma[1, #-1] == 5*EulerPhi[ #]&] (* Harvey P. Dale, Jun 22 2021 *)
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PROG
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(PARI) isok(m) = (m>1) && (sigma(m+1)+sigma(m-1) == 5*eulerphi(m)); \\ Michel Marcus, Feb 17 2021
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CROSSREFS
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KEYWORD
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easy,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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