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

Author

Colin Barker, Nov 21 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

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

Programs

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