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A039768
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Numbers k such that gcd(phi(k), k-1) = number of divisors of (k-1).
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1
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2, 3, 105, 133, 153, 185, 345, 377, 425, 585, 637, 665, 777, 805, 825, 873, 897, 905, 949, 1017, 1090, 1113, 1209, 1225, 1261, 1305, 1309, 1385, 1449, 1525, 1545, 1573, 1645, 1681, 1785, 1813, 1833, 1865, 1885, 1957, 1981, 2009, 2057, 2077, 2105
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OFFSET
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1,1
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LINKS
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EXAMPLE
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phi(105)=48, gcd(48,104)=8, 104 is divisible by {1,2,4,8,13,26,52,104}.
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MATHEMATICA
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aQ[n_] := GCD[EulerPhi[n], n - 1] == DivisorSigma[0, n - 1]; Select[Range[2, 2110], aQ] (* Amiram Eldar, Aug 28 2019 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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