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A316467 Matula-Goebel numbers of locally stable rooted identity trees, meaning no branch is a subset of any other branch of the same root. 9
1, 2, 3, 5, 11, 15, 31, 33, 47, 55, 93, 127, 137, 141, 155, 165, 211, 257, 341, 381, 411, 465, 487, 633, 635, 709, 771, 773, 811, 907, 977, 1023, 1055, 1285, 1297, 1397, 1457, 1461, 1507, 1621, 1705, 1905, 2127, 2293, 2319, 2321, 2433, 2621, 2721, 2833, 2931 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A prime index of n is a number m such that prime(m) divides n. A number belongs to this sequence iff it is squarefree, its distinct prime indices are pairwise indivisible, and its prime indices also belong to this sequence.

LINKS

Table of n, a(n) for n=1..51.

EXAMPLE

165 = prime(2)*prime(3)*prime(5) belongs to the sequence because it is squarefree, the indices {2,3,5} are pairwise indivisible, and each of them already belongs to the sequence.

Sequence of locally stable rooted identity trees preceded by their Matula-Goebel numbers begins:

    1: o

    2: (o)

    3: ((o))

    5: (((o)))

   11: ((((o))))

   15: ((o)((o)))

   31: (((((o)))))

   33: ((o)(((o))))

   47: (((o)((o))))

   55: (((o))(((o))))

   93: ((o)((((o)))))

  127: ((((((o))))))

  137: (((o)(((o)))))

  141: ((o)((o)((o))))

  155: (((o))((((o)))))

  165: ((o)((o))(((o))))

MATHEMATICA

primeMS[n_]:=If[n===1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

ain[n_]:=And[Select[Tuples[primeMS[n], 2], UnsameQ@@#&&Divisible@@#&]=={}, SquareFreeQ[n], And@@ain/@primeMS[n]];

Select[Range[100], ain]

CROSSREFS

Cf. A000081, A004111, A007097, A276625, A277098, A285572, A285573, A302796, A303362, A304713, A316468, A316469, A316471, A316474, A316476, A316494.

Sequence in context: A004680 A230147 A324855 * A282238 A004690 A001882

Adjacent sequences:  A316464 A316465 A316466 * A316468 A316469 A316470

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jul 04 2018

STATUS

approved

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Last modified October 19 12:05 EDT 2019. Contains 328217 sequences. (Running on oeis4.)