A250400 - OEIS

%I #7 Nov 21 2014 07:48:02

%S 1,16,504,1680,27300,87360,1936480,24344320,1232431200,1369368000,

%T 46695448800,865988323200,34711698621600,37381829284800,

%U 1722234277764000,21126073807238400,157125173941335600,55455943744000800,5321529955232400,162446703896568000

%N Numerator of the harmonic mean of the first n octagonal numbers.

%H Colin Barker, <a href="/A250400/b250400.txt">Table of n, a(n) for n = 1..1000</a>

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

%o (PARI)

%o harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])

%o s=vector(30); for(n=1, #s, s[n]=numerator(harmonicmean(vector(n, k, 3*k^2-2*k)))); s

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

%K nonn

%O 1,2

%A _Colin Barker_, Nov 21 2014