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A061279
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Sum_{k >= 0} 2^k*binomial(k+2,n-2*k).
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4
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1, 2, 3, 6, 10, 18, 32, 56, 100, 176, 312, 552, 976, 1728, 3056, 5408, 9568, 16928, 29952, 52992, 93760, 165888, 293504, 519296, 918784, 1625600, 2876160, 5088768, 9003520, 15929856, 28184576, 49866752, 88228864, 156102656
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| a(n) counts (binary) bit strings of length n in which no odd length block of 0's is followed by an odd length block of 1's. - Len Smiley (smiley(AT)math.uaa.alaska.edu), Nov 23 2001
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REFERENCES
| I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, Wiley, N.Y., 1983,(2.4.6).
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (0,2,2).
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FORMULA
| G.f.: (1+x)^2/(1-2*x^2-2*x^3).
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CROSSREFS
| Sequence in context: A011957 A019436 A147852 * A018073 A181649 A052972
Adjacent sequences: A061276 A061277 A061278 * A061280 A061281 A061282
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KEYWORD
| easy,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 04 2001
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EXTENSIONS
| More terms from Frank.Ellermann(AT)t-online.de, Jun 13 2001
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