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Search: id:A094559
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| A094559 |
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Number of words of length n over an alphabet of size 4 that are not "bifix-free". |
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+0
3
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| 0, 0, 4, 16, 76, 304, 1264, 5056, 20404, 81616, 327184, 1308736, 5237776, 20951104, 83815744, 335262976, 1341097036, 5364388144, 21457733104, 85830932416, 343324451056, 1373297804224, 5493194102464, 21972776409856, 87891117178864
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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Equals 4^n - A019309(n).
a(0)=a(1)=0, a(2n)=4^n + 4a(2n-1) - a(n), a(2n+1)=4a(2n). - Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 04 2006
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MAPLE
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a:=proc(n) if n=0 or n=1 then 0 elif n mod 2 = 0 then 4*a(n-1)-a(n/2)+4^(n/2) else 4*a(n-1) fi end: seq(a(n), n=0..28); (Deutsch)
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CROSSREFS
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See A019308, A019309 and A003000 for much more information. Cf. A094578.
Adjacent sequences: A094556 A094557 A094558 this_sequence A094560 A094561 A094562
Sequence in context: A109957 A101205 A050540 this_sequence A049426 A057725 A020051
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KEYWORD
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nonn,easy
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AUTHOR
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njas, Jun 06 2004
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 04 2006
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