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A109044
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a(n) = lcm(n,3).
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6
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0, 3, 6, 3, 12, 15, 6, 21, 24, 9, 30, 33, 12, 39, 42, 15, 48, 51, 18, 57, 60, 21, 66, 69, 24, 75, 78, 27, 84, 87, 30, 93, 96, 33, 102, 105, 36, 111, 114, 39, 120, 123, 42, 129, 132, 45, 138, 141, 48, 147, 150, 51, 156, 159, 54, 165, 168, 57, 174, 177, 60, 183, 186, 63
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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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a(n) = 3*n/gcd(n,3) = 3*n/A109007(n).
G.f.: 3*x*(1+2*x+x^2+2*x^3+x^4)/(1-x^3)^2.
a(n) = n*(7-2*A099837(n))/3 for n>0. (End)
a(n) = 2*a(n-3) - a(n-6) for n>5.
a(n) = 9*n/(5 + 4*cos(2*n*Pi/3)).
If n mod 3 = 0 then 3*floor(n/3), else 3*n. (End)
G.f.: 3 * x / (1 - x)^2 - 6 * x^3 / (1 - x^3)^2. -
a(n) = a(-n) for all n in Z. (End)
Sum_{k=1..n} a(k) ~ (7/6) * n^2. - Amiram Eldar, Nov 26 2022
Sum_{n>=1} (-1)^(n+1)/a(n) = 5*log(2)/9. - Amiram Eldar, Sep 08 2023
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EXAMPLE
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G.f. = 3*x + 6*x^2 + 3*x^3 + 12*x^4 + 15*x^5 + 6*x^6 + 21*x^7 + 24*x^8 + ...
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MAPLE
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MATHEMATICA
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PROG
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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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STATUS
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approved
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