A373530 Numbers k such that k, k+1 and k+2 all have at least three divisors with the same value of the Euler totient function (A000010).
14052608, 83025998, 87703714, 93978520, 117345150, 163338174, 213589088, 218539880, 294321950, 369698434, 401177798, 463425920, 470217824, 497434040, 529524918, 539318438, 554556078, 559474838, 581302358, 584754848, 608842934, 612448640, 617445814, 625591966
Offset: 1
Keywords
Programs
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Mathematica
q[n_] := Max[Tally[EulerPhi[Divisors[n]]][[;; , 2]]] > 2; seq[kmax_] := Module[{s = {}, q1 = 0, q2 = 0, q3}, Do[q3 = q[k]; If[q1 && q2 && q3, AppendTo[s, k-2]]; q1=q2; q2=q3, {k, 3, kmax}]; s]; seq[10^8] SequencePosition[Table[If[Max[Tally[EulerPhi[Divisors[n]]][[;;,2]]]>2,1,0],{n,88*10^6}],{1,1,1}] [[;;,1]] (* The program generates the first 3 terms of the sequence. *) (* Harvey P. Dale, Sep 01 2024 *) -
PARI
is(k) = vecmax(matreduce(apply(x->eulerphi(x), divisors(k)))[,2]) > 2; lista(kmax) = {my(q1 = 0, q2 = 0, q3); for(k = 3, kmax, q3 = is(k); if(q1 && q2 && q3, print1(k-2, ", ")); q1 = q2; q2 = q3);}
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