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 A301866 Numbers k such that iphi(k) = iphi(k+1), where iphi is the infinitary totient function (A064380). 1
 1, 21, 143, 208, 314, 459, 957, 1652, 2685, 5091, 20155, 38180, 41265, 45716, 54722, 116937, 161001, 186794, 230390, 274533, 338547, 416577, 430137, 495187 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(16) > 10^5. - Robert Price, May 22 2018 LINKS Table of n, a(n) for n=1..24. EXAMPLE iphi(21) = iphi(22) = 14, thus 21 is in the sequence. MATHEMATICA 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 *) CROSSREFS Cf. A064379, A064380. Sequence in context: A107731 A003702 A221785 * A101645 A230692 A267992 Adjacent sequences: A301863 A301864 A301865 * A301867 A301868 A301869 KEYWORD nonn,more AUTHOR Amiram Eldar, Mar 28 2018 EXTENSIONS a(11)-a(15) from Robert Price, May 22 2018 a(16)-a(24) from Amiram Eldar, Mar 26 2023 STATUS approved

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Last modified December 2 23:17 EST 2023. Contains 367526 sequences. (Running on oeis4.)