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A274168 Number of real integers in n-th generation of tree T(r) defined in Comments, where r^2 = -r - 1 (i.e., r = (-1 + sqrt(3))/2). 1
1, 1, 1, 1, 1, 1, 2, 2, 3, 3, 5, 5, 7, 9, 13, 18, 25, 33, 43 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

Let T* be the infinite tree with root 0 generated by these rules:  if p is in T*, then p+1 is in T* and x*p is in T*.  Let g(n) be the set of nodes in the n-th generation, so that g(0) = {0}, g(1) = {1}, g(2) = {2,x}, g(3) = {3,2x,x+1,x^2}, etc.  Let T(r) be the tree obtained by substituting r for x.

See A274142 for a guide to related sequences.

LINKS

Table of n, a(n) for n=0..18.

EXAMPLE

If r = (-1 + sqrt(3))/2), then g(3) = {3,2r,r+1, r^2}, in which the number of real integers is a(3) = 1.

MATHEMATICA

z = 18; t = Join[{{0}}, Expand[NestList[DeleteDuplicates[Flatten[Map[{# + 1, x*#} &, #], 1]] &, {1}, z]]];

u = Table[t[[k]] /. x -> (-1 + 3 I)/2, {k, 1, z}]; Table[

Count[Map[IntegerQ, u[[k]]], True], {k, 1, z}]

CROSSREFS

Cf. A274142.

Sequence in context: A027189 A140829 A184324 * A116575 A244800 A275972

Adjacent sequences:  A274165 A274166 A274167 * A274169 A274170 A274171

KEYWORD

nonn,more

AUTHOR

Clark Kimberling, Jun 13 2016

STATUS

approved

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Last modified July 6 23:56 EDT 2020. Contains 335484 sequences. (Running on oeis4.)