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A250400
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Numerator of the harmonic mean of the first n octagonal numbers.
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3
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1, 16, 504, 1680, 27300, 87360, 1936480, 24344320, 1232431200, 1369368000, 46695448800, 865988323200, 34711698621600, 37381829284800, 1722234277764000, 21126073807238400, 157125173941335600, 55455943744000800, 5321529955232400, 162446703896568000
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(3) = 504 because the first 3 octagonal numbers are [1,8,21], and 3/(1/1+1/8+1/21) = 504/197.
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PROG
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(PARI)
harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
s=vector(30); for(n=1, #s, s[n]=numerator(harmonicmean(vector(n, k, 3*k^2-2*k)))); s
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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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