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 A265120 Irregular array read by rows: Row n gives the number of elements in the multiplicative group mod n, (Z/nZ, *), that have order d for each divisor d of the exponent of the group. 0
 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1, 3, 1, 1, 2, 2, 1, 1, 2, 1, 1, 4, 4, 1, 3, 1, 1, 2, 2, 2, 4, 1, 1, 2, 2, 1, 3, 4, 1, 3, 4, 1, 1, 2, 4, 8, 1, 1, 2, 2, 1, 1, 2, 2, 6, 6, 1, 3, 4, 1, 3, 2, 6, 1, 1, 4, 4, 1, 1, 10, 10, 1, 7, 1, 1, 2, 4, 4, 8 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,8 COMMENTS The exponent of the multiplicative group mod n is Carmichael lambda(n) given in A002322. The row lengths are tau(lambda(n)) = A000005(A002322(n)) = A066800(n). The invariant factor decomposition of (Z/nZ,*) is given in A258446. The row sums are phi(n) = A000010(n). It appears that column 2 is A155828. LINKS EXAMPLE {1} {1, 1} {1, 1} {1, 1, 2} {1, 1} {1, 1, 2, 2} {1, 3} {1, 1, 2, 2} {1, 1, 2} {1, 1, 4, 4} {1, 3} {1, 1, 2, 2, 2, 4} {1, 1, 2, 2} {1, 3, 4} {1, 3, 4} {1, 1, 2, 4, 8} {1, 1, 2, 2} {1, 1, 2, 2, 6, 6} {1, 3, 4} {1, 3, 2, 6} {1, 1, 4, 4} {1, 1, 10, 10} {1, 7}, {1, 1, 2, 4, 4, 8} The row for n=21 reads: 1,3,2,6 because the multiplicative group mod 21,  (Z/21*Z,*) is isomorphic to C_6 X C_2. The exponent of this group is 6. This group contains one element of order 1, three elements of order 2, two elements of order 3, and six elements of order 6. MATHEMATICA f[{p_, e_}] := {FactorInteger[p - 1][[All, 1]]^     FactorInteger[p - 1][[All, 2]],    FactorInteger[p^(e - 1)][[All, 1]]^     FactorInteger[p^(e - 1)][[All, 2]]}; fun[lst_] := Module[{int, num, res},   int = Sort /@ GatherBy[Join @@ (FactorInteger /@ lst), First];   num = Times @@ Power @@@ (Last@# & /@ int);   res = Flatten[Map[Power @@ # &, Most /@ int, {2}]];   {num, res}] rec[lt_] := First@NestWhile[{Append[#[[1]], fun[#[[2]]][[1]]],      fun[#[[2]]][[2]]} &, {{}, lt}, Length[#[[2]]] > 0 &]; t[list_] := Table[Count[Map[PermutationOrder, GroupElements[AbelianGroup[list]]],     d], {d, Divisors[First[list]]}]; Map[t, Table[    If[! IntegerQ[n/8],     DeleteCases[rec[Flatten[Map[f, FactorInteger[n]]]], 1],     DeleteCases[      rec[Join[{2, 2^(FactorInteger[n][[1, 2]] - 2)},        Flatten[Map[f, Drop[FactorInteger[n], 1]]]]], 1]], {n, 2,     25}] /. {} -> {1}] CROSSREFS Cf. A000005, A000010, A002322, A066800, A155828, A258446. Sequence in context: A296773 A108244 A277824 * A124961 A008967 A211355 Adjacent sequences:  A265117 A265118 A265119 * A265121 A265122 A265123 KEYWORD nonn,tabf AUTHOR Geoffrey Critzer, Dec 01 2015 STATUS approved

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Last modified July 20 05:56 EDT 2019. Contains 325168 sequences. (Running on oeis4.)