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

1,2

Comments

Also Matula-Goebel numbers of lone-child-avoiding rooted trees at with at most one non-leaf branch under any given vertex. A rooted tree is lone-child-avoiding if there are no unary branchings. The Matula-Goebel number of a rooted tree is the product of primes indexed by the Matula-Goebel numbers of the branches of the root, which gives a bijective correspondence between positive integers and unlabeled rooted trees.

Also Matula-Goebel numbers of lone-child-avoiding locally disjoint semi-identity trees. Locally disjoint means no branch of any vertex overlaps a different (unequal) branch of the same vertex. In a semi-identity tree, all non-leaf branches of any given vertex are distinct.

Links

Robert Israel, Table of n, a(n) for n = 1..3140

Formula

Intersection of A291636, A316495, and A306202.

Example

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))

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

Mathematica

uryQ[n_]:=n==1||MatchQ[FactorInteger[n], ({{2, _}, {p_, 1}}/; uryQ[PrimePi[p]])|({{2, k_}}/; k>1)];
Select[Range[100], uryQ]

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.

Unlabeled semi-identity trees are counted by A306200, with Matula-Goebel numbers A306202.

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.

Cf. A000081, A007097, A061775, A196050, A276625, A316470, A316696, A331678, A331679, A331680, A331682, A331686, A331687.

Sequence in context: A320269 A331871 A331965 * A036312 A312338 A312339

Adjacent sequences: A331680 A331681 A331682 * A331684 A331685 A331686

Keyword

nonn

Author

Gus Wiseman, Jan 30 2020

Status

approved