OFFSET
1,2
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
EXAMPLE
Taking the first generation of edges of the tree to be G(1) = {(1,2)}, the edge (1,2) grows G(2) = {(2,3), (2,5), (2,7)}, which grows G(3) = {(3,5), (3,8), (3,11), (5,7), (5,12), (5,17), (7,9), (7,16), (7,23)}, ... Expelling duplicate nodes and sorting leave {1,2,3,5,7,8,9,...}.
MATHEMATICA
f[x_, y_] := {{y, x + y}, {y, x + 2 y}}; x = 2; y = 3; t = {{x, y}};
u = Table[t = Flatten[Map[Apply[f, #] &, t], 1], {12}]; v = Flatten[u];
w = Flatten[Prepend[Table[v[[2 k]], {k, 1, Length[v]/2}], {x, y}]];
Sort[Union[w]]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 05 2013
STATUS
approved