A214641 Indices of a in the sequence closed under a -> abc, b -> ab, c -> b . Start with a.

1, 4, 7, 10, 12, 14, 17, 20, 23, 25, 28, 30, 33, 36, 39, 41, 43, 46, 49, 52, 54, 57, 60, 63, 65, 68, 71, 74, 76, 78, 81, 84, 87, 89, 92, 94, 97, 100, 103, 105, 107, 110, 113, 116, 118, 121, 124, 127, 129, 131, 134, 137, 140, 142, 145, 148, 151, 153, 155, 158

Offset: 1

Author

Philippe Deléham, Jul 23 2012

Keywords

• nonn

Comments

Indices of 1 in A214640.

Examples

			a -> abc -> abcabb -> abcabbabcabab -> abcabbabcabababcabbabcababcab -> ...
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A214640, A214642, A214644.

Programs

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))Alois P. Heinz, Jul 28 2012

Mathematica

SubstitutionSystem[{"a" -> {"a", "b", "c"}, "b" -> {"a", "b"}, "c" -> {"b"}}, {"a"}, 7] // Last // Position[#, "a"]& // Flatten (* Jean-François Alcover, Nov 04 2020 *)