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A087211
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a(n) = floor((1+2^n+3^n)/3).
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1
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1, 2, 4, 12, 32, 92, 264, 772, 2272, 6732, 20024, 59732, 178512, 534172, 1599784, 4793892, 14370752, 43090412, 129227544, 387595252, 1162610992, 3487483452, 10461751304, 31383855812, 94148771232, 282440721292, 847310979064
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: (1-2*x-3*x^2+4*x^3)/((1+x)*(1-2*x)*(1-3*x));
E.g.f.: (exp(3*x)+exp(2*x)+2*exp(0)-exp(-x))/3;
a(n) = (3^n+2^n+2*0^n-(-1)^n)/3.
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MATHEMATICA
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Table[Floor[(1+2^n+3^n)/3], {n, 0, 30}] (* or *) LinearRecurrence[{4, -1, -6}, {1, 2, 4, 12}, 30] (* Harvey P. Dale, May 21 2018 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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