A135156 a(n) = number of strings of length n that can be obtained by starting with abc and repeatedly doubling any substring of length >= 2 in place.

1, 0, 2, 0, 3, 1, 4, 0, 5, 2, 6, 1, 7, 3, 8, 9, 9, 7, 10, 34, 11, 36, 12, 136, 13, 190, 14, 567, 15, 1018, 16, 2445, 17, 5474, 18, 11371, 19, 28233, 20, 57961, 21, 143391, 22, 308793, 23, 740519, 24, 1668316

Offset: 0

Author

David Applegate and N. J. A. Sloane, Feb 15 2008

Keywords

• nonn

Comments

A "weakly primitive" version of A135473. Cf. A135017.

Differs from A135017 in that the strings may contain repeated letters.

Links

• Index entries for doubling substrings