OFFSET
1,1
COMMENTS
Indices of 3 in A214640.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
EXAMPLE
Start: a
Rules:
a --> abc
b --> ab
c --> b
-------------
0: (#=1)
a
1: (#=3)
abc
2: (#=6)
abcabb
3: (#=13)
abcabbabcabab
4: (#=29)
abcabbabcabababcabbabcababcab
5: (#=64)
abcabbabcabababcabbabcababcababcabbabcabababcabbabcababcabbabcab
3 9 16 22 27 ... (positions of 'c')
MAPLE
S:= proc(n) option remember; `if`(n=0, [1], subs(x=[1, 2, 3][],
y=[1, 2][], z=2, subs(1=x, 2=y, 3=z, S(n-1))))
end:
a:= proc(n) option remember; local i, k; i:=1;
for k from 1+`if`(n=1, 0, a(n-1)) do
while nops(S(i))<k do i:=i+1 od;
if S(i)[k] = 3 then return k fi
od
end:
seq(a(n), n=1..100); # Alois P. Heinz, Jul 28 2012
MATHEMATICA
SubstitutionSystem[{"a" -> {"a", "b", "c"}, "b" -> {"a", "b"}, "c" -> {"b"}}, {"a"}, 8] // Last // Position[#, "c"]& // Flatten (* Jean-François Alcover, Nov 04 2020 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Jul 24 2012
STATUS
approved