A250344 Numerator of the harmonic mean of the first n hexagonal numbers.

1, 12, 90, 1680, 6300, 83160, 1261260, 576576, 11027016, 1163962800, 1280359080, 32125373280, 174012438600, 80313433200, 2495453103000, 165032631878400, 175347171370800, 1299631976042400, 50757848842100400, 53429314570632000, 2300131992265707600

Offset

1,2

Links

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

Example

a(3) = 90 because the first 3 hexagonal numbers are [1,6,15], and 3/(1/1+1/6+1/15) = 90/37.

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, k*(2*k-1))))); s

Crossrefs

Cf. A000384 (hexagonal numbers), A082687 (denominators).

Sequence in context: A249979 A374424 A231512 * A135173 A173223 A114860

Adjacent sequences: A250341 A250342 A250343 * A250345 A250346 A250347

Keyword

nonn

Author

Colin Barker, Nov 19 2014

Status

approved