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A284406
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Odd numbers k such that lambda(k) < phi(k) and gcd(lambda(k), k-1) = gcd(phi(k), k-1).
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1
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15, 35, 39, 45, 51, 55, 63, 75, 85, 87, 95, 99, 111, 115, 117, 119, 123, 135, 143, 147, 153, 155, 159, 165, 171, 175, 183, 187, 195, 203, 205, 207, 215, 219, 221, 231, 235, 245, 247, 255, 259, 261, 267, 275, 279, 285, 287, 291, 295, 299, 303, 315, 319, 323, 325, 327, 333, 335, 339, 351
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OFFSET
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1,1
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COMMENTS
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If odd n is in A033949 and n-1 is squarefree, then n is in the sequence.
The set of such numbers has a positive natural density.
The density is 1/2. Almost all odd numbers have this property.
The number of terms below 10^k for k = 1, 2, ... are 0, 12, 204, 2507, 27801, 296583, 3102205, 32054920, 328714616, 3353406273, .... Apparently the asymptotic density of this sequence is less than 1/2. - Amiram Eldar, Jul 14 2020
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LINKS
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MATHEMATICA
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Select[Range[1, 351, 2], Function[k, And[#1 < #2, GCD[#1, k - 1] == GCD[#2, k - 1]] & @@ {CarmichaelLambda@ k, EulerPhi@ k}]] (* Michael De Vlieger, Mar 26 2017 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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