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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. 11
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
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[#]&]
PROG
(PARI) is(n) = while((n>>=valuation(n, 2)) > 1, isprimepower(n, &n) || return(0); n=primepi(n)); 1; \\ Kevin Ryde, Apr 04 2021
CROSSREFS
Sequence in context: A285801 A324109 A070776 * A076564 A325044 A343822
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 08 2018
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)