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Search: id:A120926
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| A120926 |
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Number of isolated 0's in all ternary words of length n on {0,1,2}. |
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+0
2
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| 1, 4, 16, 60, 216, 756, 2592, 8748, 29160, 96228, 314928, 1023516, 3306744, 10628820, 34012224, 108413964, 344373768, 1090516932, 3443737680, 10847773692, 34093003032, 106928054964, 334731302496, 1046035320300
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OFFSET
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1,2
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COMMENT
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a(n)=Sum(k*A120924(n,k),k=0..ceil(n/2)).
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FORMULA
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a(n)=(4/27)(n+1)3^n for n>=2. G.f.=z(1-z)^2/(1-3z)^2.
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EXAMPLE
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a(2)=4 because in the 9 ternary words of length 2, namely 00,01,02,10,11,12,20,21, and 22, we have altogether 4 isolated 0's.
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MAPLE
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1, seq(4*(n+1)*3^n/27, n=2..28);
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CROSSREFS
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Cf. A120924.
Adjacent sequences: A120923 A120924 A120925 this_sequence A120927 A120928 A120929
Sequence in context: A119827 A089883 A089932 this_sequence A128650 A072335 A081161
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 16 2006
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