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A276402
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A sequence related to the Somos-6 sequence A006722.
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1
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1, 1, -1, 1, -3, -3, 1, -25, 49, 1, 385, 1489, 503, 10753, -82371, -196419, -1575551, -12482641, 95770849, -739310591, 5684060161, 45018762529, 359479836623, 7751171129473, -59488778593731, -137028961472835, -29749898850946559, -441962130410844841
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OFFSET
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0,5
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COMMENTS
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This is the right-hand portion of a two-way infinite sequence ..., 1, -1, 1, 1, 1, 1, -1, 1, -3, -3, 1, -25, 49, 1, 385, 1489, 503, 10753, -82371, ...
0 = a(n+5)*a(n-4) + 2*a(n+4)*a(n-3) - 2*a(n+3)*a(n-2) - 4*a(n+2)*a(n-1) - 5*a(n+1)*a(n) = 2*a(n+5)*a(n-5) + 4*a(n+4)*a(n-4) + 5*a(n+3)*a(n-3) + 19*a(n+2)*a(n-2) + 18*a(n+1)*a(n-1) for all n in Z. - Michael Somos, Aug 14 2023
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LINKS
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FORMULA
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a(0) = a(1) = 1, a(2) = -1, a(3) = 1, a(4) = a(5)= -3, a(n+6)*a(n) = a(n+5)*a(n+1) + 2*a(n+4)*a(n+2) - 2*a(n+3)^2. - Seiichi Manyama, Sep 12 2016
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MATHEMATICA
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a[0] = a[1] = 1; a[2] = -1; a[3] = 1; a[4] = a[5] = -3;
a[n_] := a[n] = (-2a[n-3]^2 + 2a[n-4] a[n-2] + a[n-5] a[n-1])/a[n-6];
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PROG
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(PARI) {a(n) = if( n>-1 && n<3, [1, 1, -1][n+1], if( n<0, a(-1-n), (a(n-1)*a(n-5) + 2*a(n-2)*a(n-4) - 2*a(n-3)*a(n-3)) / a(n-6)))}; /* Michael Somos, Aug 14 2023 */
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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