A250344 - OEIS

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

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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