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A140787
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2^n*(n/3+11/18) + (-1)^n* (2^(n-1)-1/9).
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1
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1, 1, 7, 9, 39, 57, 199, 313, 967, 1593, 4551, 7737, 20935, 36409, 94663, 167481, 422343, 757305, 1864135, 3378745, 8155591, 14913081, 35418567, 65244729, 152859079, 283348537, 656175559, 1222872633, 2803659207, 5249404473
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OFFSET
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0,3
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COMMENTS
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Based on pair reversal of Jacobsthal numbers and successive differences (*).
(*) First three are A092808, A094359, A140505.
Consider low triangle 1; 0, 1; 2, -1, 4; -2, 3, 0, 4; 6, -5, 8, -4, 16; -10, 11, -8, 12, 0, 16; a(n) is absolute rows sum.
Note triangle's rows sum: b(n)= 1, 1, 5, 5, 21, 21 =A052992.
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index to sequences with linear recurrences with constant coefficients, signature (1,6,-4,-8).
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FORMULA
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a(n+1)-2a(n)= -1, 5, -5, 21, -21, 85, -85 essentially doubled A001045(2n) signed.
G.f. 1 / ( (1+x)*(2*x+1)*(-1+2*x)^2 ). - R. J. Mathar, Jul 02 2011
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PROG
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(MAGMA) [2^n*(n/3+11/18) + (-1)^n* (2^(n-1)-1/9): n in [0..40]]; // Vincenzo Librandi, Aug 08 2011
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CROSSREFS
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Sequence in context: A083203 A082536 A057590 * A032695 A007449 A189053
Adjacent sequences: A140784 A140785 A140786 * A140788 A140789 A140790
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KEYWORD
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nonn,easy,uned
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AUTHOR
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Paul Curtz, Jul 14 2008
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STATUS
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approved
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