The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A135017 a(n) = number of strings of length n that can be obtained by starting with abc and repeatedly doubling any substring in place and then discarding any string that contains two successive equal letters. 4
 0, 0, 1, 0, 2, 1, 3, 5, 7, 15, 20, 48, 60, 156, 205, 489, 761, 1572, 2796, 5357, 10174, 19021, 37272, 69375, 137759, 258444, 513696, 976890, 1934900, 3727164, 7358675, 14316861, 28217028, 55288907, 108942267, 214462953, 422973649 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS These strings may be regarded as the "primitive" strings among those enumerated by A135473. Equals the inverse binomial transform of A135473. LINKS FORMULA Empirically, grows like 2^n. EXAMPLE n=3: abc n=4: - n=5: ababc, abcbc n=6: abcabc n=7: abababc, ababcbc, abcbcbc CROSSREFS Cf. A135473. Sequence in context: A076074 A319153 A286390 * A070168 A246646 A198094 Adjacent sequences:  A135014 A135015 A135016 * A135018 A135019 A135020 KEYWORD nonn AUTHOR David Applegate and N. J. A. Sloane, Feb 12 2008 EXTENSIONS Extended to 37 terms by David Applegate, Feb 16 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 5 11:52 EDT 2020. Contains 334840 sequences. (Running on oeis4.)