A250400 Numerator of the harmonic mean of the first n octagonal numbers.

1, 16, 504, 1680, 27300, 87360, 1936480, 24344320, 1232431200, 1369368000, 46695448800, 865988323200, 34711698621600, 37381829284800, 1722234277764000, 21126073807238400, 157125173941335600, 55455943744000800, 5321529955232400, 162446703896568000

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Example

a(3) = 504 because the first 3 octagonal numbers are [1,8,21], and 3/(1/1+1/8+1/21) = 504/197.

Prog

(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

Crossrefs

Cf. A000567 (octagonal numbers), A250401 (denominators).

Sequence in context: A209057 A209214 A183890 * A214624 A322888 A291852

Adjacent sequences: A250397 A250398 A250399 * A250401 A250402 A250403

Keyword

nonn

Author

Colin Barker, Nov 21 2014

Status

approved