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A118648
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a(n) is the number of binary strings of length n+3 such that there exist a subsequence of length 4 with 2 ones in it.
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0
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11, 25, 54, 114, 237, 486, 988, 1998, 4027, 8097, 16253, 32587, 65286, 130727, 261668, 523631, 1047669, 2095900, 4192576, 8386223, 16773924, 33549888, 67102592, 134209071, 268423507, 536854419, 1073719059, 2147452226
(list; graph; refs; listen; history; internal format)
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OFFSET
| 4,1
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COMMENTS
| a(n) = 2^(n+4) - sum of all elements of the n-th power of the matrix [[1 1 0 0 0] [0 0 1 0 0] [0 0 0 1 0] [0 0 0 0 1] [1 1 0 0 0]] which is the transition matrix for the last four bits being 0000, 0001, 0010, 0100, 1000. - Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Aug 04 2006
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (3,-2,0,1,-2).
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FORMULA
| G.f. -x^4*(-11+8*x-x^2-2*x^3+8*x^4) / ( (2*x-1)*(x^4+x-1) ). - R. J. Mathar, Nov 28 2011
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CROSSREFS
| Sequence in context: A031025 A140675 A161532 * A105270 A039337 A043160
Adjacent sequences: A118645 A118646 A118647 * A118649 A118650 A118651
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KEYWORD
| nonn
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AUTHOR
| Tanya Khovanova (tanyakh(AT)yahoo.com), May 10 2006
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