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A330871
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Numbers k such that k and k+1 are both phi-practical numbers (A260653).
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3
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1, 2, 3, 15, 255, 735, 2624, 3135, 4095, 4784, 5264, 5984, 7215, 7424, 7904, 9344, 10064, 10335, 10815, 11024, 11984, 12375, 12495, 13695, 16184, 16575, 22575, 22784, 22815, 26144, 26264, 27104, 30015, 30855, 30975, 32384, 33824, 34335, 34544, 38024, 38415, 39104
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OFFSET
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1,2
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LINKS
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EXAMPLE
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1 is a term since both 1 and 2 are phi-practical numbers.
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MATHEMATICA
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phiPracticalQ[n_] := If[n<1, False, If[n==1, True, (lst = Sort @ EulerPhi @ Divisors[n]; ok=True; Do[If[lst[[m]]>Sum[lst[[l]], {l, 1, m-1}]+1, (ok=False; Break[])], {m, 1, Length[lst]}]; ok)]]; Select[Range[40000], phiPracticalQ[#] && phiPracticalQ[#+1] &] (* after Frank M Jackson at A260653 *)
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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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