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A301866
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Numbers k such that iphi(k) = iphi(k+1), where iphi is the infinitary totient function (A064380).
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1
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1, 21, 143, 208, 314, 459, 957, 1652, 2685, 5091, 20155, 38180, 41265, 45716, 54722, 116937, 161001, 186794, 230390, 274533, 338547, 416577, 430137, 495187
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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iphi(21) = iphi(22) = 14, thus 21 is in the sequence.
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MATHEMATICA
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irelprime[n_] := Select[temp = iDivisors[n]; Range[n], Intersection[iDivisors[#], temp] === {1} &]; bitty[k_] := Union[Flatten[Outer[Plus, Sequence @@ {0, #1} & /@ Union[2^Range[0, Floor[Log[2, k]]]*Reverse[IntegerDigits[k, 2]]]]]];
iDivisors[k_Integer] := Sort[(Times @@ (First[it]^(#1 /. z -> List)) &) /@ Flatten[Outer[z, Sequence @@ bitty /@ Last[it = Transpose[FactorInteger[k]]], 1]]]; iDivisors[1] := {1}; iphi[n_] := Length[irelprime[n]]; iphiQ[n_] := iphi[n] == iphi[n + 1]; Select[Range[10^3], iphiQ](* after Wouter Meeussen at A064379 *)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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