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A182453
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a(n) = 3^n - n*(n-1)/2.
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0
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1, 3, 8, 24, 75, 233, 714, 2166, 6533, 19647, 59004, 177092, 531375, 1594245, 4782878, 14348802, 43046601, 129140027, 387420336, 1162261296, 3486784211, 10460352993, 31381059378, 94143178574, 282429536205, 847288609143, 2541865828004, 7625597484636, 22876792454583, 68630377364477, 205891132094214, 617673396283482, 1853020188851345, 5559060566554995
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OFFSET
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0,2
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COMMENTS
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For n>0, r(n)=a(n)/a(n-1) is approximately equal to 3. Average of the sum of r(n) is 3. Except for r(3) = 2.666666666666667, all other r(n)'s are just above zero and r(n) tends to 3 as n tends to infinity.
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LINKS
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FORMULA
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G.f.: (1-3*x+2*x^2+2*x^3)/((1-x)^3*(1-3*x)). - Colin Barker, May 07 2012
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EXAMPLE
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For n=6, a(n)=714, a(n-1)=233, r(n)=3.0643776824034334763948497854077.
For n=21, a(n)=10460352993, a(n-1)=3486784211, r(n) = 3.0000001032469972946083183924341.
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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