A331683 One and all numbers of the form 2^k * prime(j) for k > 0 and j already in the sequence.
1, 4, 8, 14, 16, 28, 32, 38, 56, 64, 76, 86, 106, 112, 128, 152, 172, 212, 214, 224, 256, 262, 304, 326, 344, 424, 428, 448, 512, 524, 526, 608, 622, 652, 688, 766, 848, 856, 886, 896, 1024, 1048, 1052, 1154, 1216, 1226, 1244, 1304, 1376, 1438, 1532, 1696
Offset: 1
Keywords
Examples
The sequence of all lone-child-avoiding rooted trees with at most one non-leaf branch under any given vertex together with their Matula-Goebel numbers begins: 1: o 4: (oo) 8: (ooo) 14: (o(oo)) 16: (oooo) 28: (oo(oo)) 32: (ooooo) 38: (o(ooo)) 56: (ooo(oo)) 64: (oooooo) 76: (oo(ooo)) 86: (o(o(oo))) 106: (o(oooo)) 112: (oooo(oo)) 128: (ooooooo) 152: (ooo(ooo)) 172: (oo(o(oo))) 212: (oo(oooo)) 214: (o(oo(oo))) 224: (ooooo(oo))
Links
- Robert Israel, Table of n, a(n) for n = 1..3140
Crossrefs
These trees counted by number of vertices are A212804.
The semi-lone-child-avoiding version is A331681.
The non-semi-identity version is A331871.
Lone-child-avoiding rooted trees are counted by A001678.
Matula-Goebel numbers of lone-child-avoiding rooted trees are A291636.
Locally disjoint rooted trees are counted by A316473.
Matula-Goebel numbers of locally disjoint rooted trees are A316495.
Lone-child-avoiding locally disjoint rooted trees by leaves are A316697.
Programs
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Maple
N:= 10^4: # for terms <= N S:= {1}: with(queue): Q:= new(1): while not empty(Q) do r:= dequeue(Q); p:= ithprime(r); newS:= {seq(2^i*p,i=1..ilog2(N/p))} minus S; S:= S union newS; for s in newS do enqueue(Q,s) od: od: sort(convert(S,list)); # Robert Israel, Feb 05 2020
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Mathematica
uryQ[n_]:=n==1||MatchQ[FactorInteger[n],({{2,},{p,1}}/;uryQ[PrimePi[p]])|({{2,k_}}/;k>1)]; Select[Range[100],uryQ]
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