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 A206944 Numbers Phi_k(m) with integer k > 2, |m| > 1 but k != 2^j (j > 1). 1
 3, 7, 11, 13, 21, 31, 43, 57, 61, 73, 91, 111, 121, 127, 133, 151, 157, 183, 205, 211, 241, 273, 307, 331, 341, 343, 381, 421, 463, 507, 521, 547, 553, 601, 651, 683, 703, 757, 781, 813, 871, 931, 993, 1057, 1093, 1111, 1123, 1191, 1261, 1333, 1407, 1483 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Phi_k(m) denotes the cyclotomic polynomial numbers Cyclotomic(k,m). There is a property for Cyclotomic(k,m): Cyclotomic(k^(j+1),m) = Cyclotomic(k,m^(k^j)). So actually when k=2^(j+1), j is a positive integer, Cyclotomic(k,m) = Cyclotomic(2,m^(2^j)) = 1+m^(2^j). If these cases are excluded from A206942, this sequence is obtained. This sequence is a subsequence of A206942. Sequence A059054 is a subsequence of this sequence. The Mathematica program can generate this sequence to arbitrary boundary maxdata without a user's choice of parameters. The parameter determination part of this program is explained at A206864. LINKS EXAMPLE a(1) = 3 = Phi(6,2). 5 = Phi(4,2) = Phi(2,4) so excluded. a(2) = 7 = Phi(3,2). MATHEMATICA phiinv[n_, pl_] := Module[{i, p, e, pe, val}, If[pl == {}, Return[If[n == 1, {1}, {}]]]; val = {}; p = Last[pl]; For[e = 0; pe = 1, e == 0 || Mod[n, (p - 1) pe/p] == 0, e++; pe *= p, val = Join[val, pe*phiinv[If[e == 0, n, n*p/pe/(p - 1)], Drop[pl, -1]]]]; Sort[val]]; phiinv[n_] := phiinv[n, Select[1 + Divisors[n], PrimeQ]]; maxdata = 1500; max = Ceiling[(1 + Sqrt[1 + 4*(maxdata - 1)])/4]*2; eb = 2*Floor[(Log[2, maxdata])/2 + 0.5]; While[eg = phiinv[eb]; lu = Length[eg]; lu == 0, eb = eb + 2]; t = Select[Range[eg[[Length[eg]]]], ((EulerPhi[#] <= eb) && ((! IntegerQ[Log[2, #]]) || (# <= 2))) &]; ap = SortBy[t, Cyclotomic[#, 2] &]; an = SortBy[t, Cyclotomic[#, -2] &]; a = {}; Do[i = 2; While[i++; cc = Cyclotomic[ap[[i]], m]; cc <= maxdata,   a = Append[a, cc]]; i = 2; While[i++; cc = Cyclotomic[an[[i]], -m]; cc <= maxdata, a = Append[a, cc]], {m, 2, max}]; Union[a] CROSSREFS Cf. A206942, A194712, A059054, A206864. Sequence in context: A176797 A078098 A154831 * A206943 A059054 A197318 Adjacent sequences:  A206941 A206942 A206943 * A206945 A206946 A206947 KEYWORD nonn AUTHOR Lei Zhou, Feb 13 2012 STATUS approved

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Last modified September 21 16:31 EDT 2021. Contains 347598 sequences. (Running on oeis4.)