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A320230 Matula-Goebel numbers of rooted trees in which the non-leaf branches directly under any given node are all equal. 4
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 34, 36, 37, 38, 40, 41, 43, 44, 46, 48, 49, 50, 52, 53, 54, 56, 58, 59, 61, 62, 64, 67, 68, 71, 72, 74, 76, 79, 80, 81, 82, 83, 86, 88, 89, 92, 96, 97 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A number is in the sequence iff it belongs to A070776 and its prime indices already belong to the sequence. A prime index of n is a number m such that prime(m) divides n.

LINKS

Table of n, a(n) for n=1..67.

MATHEMATICA

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

smakQ[n_]:=And[SameQ@@DeleteCases[primeMS[n], 1], And@@smakQ/@DeleteCases[primeMS[n], 1]]; Select[Range[100], smakQ[#]&]

CROSSREFS

Cf. A002541, A070776, A214577, A294336, A317710, A320222, A320226.

Sequence in context: A285801 A324109 A070776 * A076564 A325044 A303550

Adjacent sequences:  A320227 A320228 A320229 * A320231 A320232 A320233

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 08 2018

STATUS

approved

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Last modified November 22 03:20 EST 2019. Contains 329383 sequences. (Running on oeis4.)