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A309874
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a(n) = 2*n*Fibonacci(n-2) + (-1)^n + 1.
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12
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2, 6, 10, 20, 38, 70, 130, 234, 422, 748, 1322, 2314, 4034, 6990, 12066, 20740, 35534, 60686, 103362, 175602, 297662, 503516, 850130, 1432850, 2411138, 4051350, 6798010, 11392244, 19068662, 31882198, 53250562, 88853754, 148125014
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OFFSET
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2,1
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COMMENTS
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For n >= 2, a(n) is the number of length n losing strings with a binary alphabet in the "same game".
In the "same game", winning strings are those that can be reduced to the null string by repeatedly removing an entire run of two or more consecutive symbols.
Sequence A035615 counts the winning strings of length n in a binary alphabet in the "same game".
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LINKS
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FORMULA
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G.f.: x^2*(2 + 2*x - 6*x^2 - 4*x^3 + 6*x^4 + 2*x^5)/((1-x^2)*(1-x-x^2)^2. - Robert Israel, Sep 03 2019
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EXAMPLE
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For n=2, we have 2^2 = 4 strings of length 2 in the binary alphabet {0,1}: 00, 11, 01, and 10. Out of those strings, only 00 and 11 are winning strings in the "same game" because removing an entire run of two or more consecutive symbols gives the null string. Thus, a(2) = 2 (corresponding to the losing strings 01 and 10).
For n=3, we have 2^3 = 8 strings of length 3 in the binary alphabet {0,1}: 000, 001, 010, 100, 110, 101, 011, 111. Out of these, only the strings 000 and 111 are winning, while the rest a(2) = 6 strings are losing strings.
For n=4, we have 2^4 = 16 strings of length 4 in the binary alphabet {0,1}. From these, only 0000, 0011, 1100, 0110, 1001, and 1111 are winning strings while the rest a(4) = 16 - 6 = 10 are losing strings. (For example 0{11}0 -> 00 -> null.)
For n=8, the string 11011001 is a winning string since 110{11}001 -> 11{000}1 -> {111} -> null.
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MAPLE
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seq(2*n*combinat:-fibonacci(n-2) + (-1)^n + 1, n=2..100); # Robert Israel, Sep 03 2019
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MATHEMATICA
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CROSSREFS
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Cf. A035615, A035617, A065237, A065238, A065239, A065240, A065241, A065242, A065243, A323812, A323844.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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