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A008382
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a(n) = floor(n/5)*floor((n+1)/5)*floor((n+2)/5)*floor((n+3)/5)*floor((n+4)/5).
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12
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0, 0, 0, 0, 0, 1, 2, 4, 8, 16, 32, 48, 72, 108, 162, 243, 324, 432, 576, 768, 1024, 1280, 1600, 2000, 2500, 3125, 3750, 4500, 5400, 6480, 7776, 9072, 10584, 12348, 14406, 16807, 19208, 21952, 25088, 28672, 32768, 36864, 41472, 46656, 52488, 59049, 65610, 72900, 81000
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OFFSET
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0,7
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COMMENTS
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For n >= 5, a(n) is the maximal product of 5 positive integers with sum n. - Wesley Ivan Hurt, Jun 29 2022
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,4,-8,4,0,0,-6,12,-6,0,0,4,-8,4,0,0,-1,2,-1).
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FORMULA
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a(n) = +2*a(n-1) -a(n-2) +4*a(n-5) -8*a(n-6) +4*a(n-7) -6*a(n-10) +12*a(n-11) -6*a(n-12) +4*a(n-15) -8*a(n-16) +4*a(n-17) -a(n-20) +2*a(n-21) -a(n-22).
G.f.: x^5 *(x^10 -2*x^9 +4*x^8 -4*x^7 +8*x^6 -8*x^5 +8*x^4 -4*x^3 +4*x^2 -2*x+1) *(1+x)^2 / ( (x^4+x^3+x^2+x+1)^4 *(x-1)^6 ). (End)
Sum_{n>=5} 1/a(n) = 1 + zeta(5). - Amiram Eldar, Jan 10 2023
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MATHEMATICA
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CoefficientList[Series[x^5*(x^10 - 2*x^9 + 4*x^8 - 4*x^7 + 8*x^6 - 8*x^5 + 8*x^4 - 4*x^3 + 4*x^2 - 2*x + 1)*(1 + x)^2/((x^4 + x^3 + x^2 + x + 1)^4*(x - 1)^6), {x, 0, 60}], x] (* Wesley Ivan Hurt, Jun 29 2022 *)
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PROG
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(Maxima) A008382(n):=floor(n/5)*floor((n+1)/5)*floor((n+2)/5)*floor((n+3)/5)*floor((n+4)/5)$
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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