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A065494
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Number of (binary) bit strings in which no even length block of 0's is followed by an even length block of 1's.
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3
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1, 2, 4, 8, 15, 30, 57, 112, 216, 420, 815, 1580, 3069, 5950, 11552, 22408, 43487, 84378, 163725, 317700, 616444, 1196172, 2321007, 4503704, 8738921, 16956954, 32903164, 63845000, 123884479, 240384374, 466440273, 905077080, 1756205088
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| O.g.f.: (1+x)^2/(1-3x^2-2x^3+x^4)
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EXAMPLE
| a(6)=64-7=57 because 000011, 001111, 001100, 001101, 100110, 010011, 110011 are forbidden.
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CROSSREFS
| Cf. A061279 (forbids odd block 0's - odd block 1's), A065455, A065495, A065497.
Sequence in context: A026023 A077596 A091865 * A134044 A079967 A192655
Adjacent sequences: A065491 A065492 A065493 * A065495 A065496 A065497
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KEYWORD
| nonn
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AUTHOR
| Len Smiley (smiley(AT)math.uaa.alaska.edu), Nov 24 2001
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