A246498 Numerator of the harmonic mean of the first n squares.

1, 8, 108, 576, 18000, 21600, 1234800, 5644800, 57153600, 12700800, 1690476480, 1844156160, 337634256960, 363606122880, 1947889944000, 8310997094400, 2551995545299200, 2702112930316800, 1029655143835718400, 216769503965414400, 4645060799258880

Offset: 1

Author

Colin Barker, Nov 14 2014

Keywords

• nonn

Examples

			a(3) = 108 because the first 3 squares are [1,4,9] and 3 / (1/1+1/4+1/9) = 108/49.
		

Links

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

Crossrefs

Cf. A007406 (denominators).

Programs

Maple

A246498 := proc(n::integer)
    n/add(1/k^2,k=1..n) ;
    numer(%) ;
end proc:
seq(A246498(n),n=1..13) ; # R. J. Mathar, Nov 05 2019

Mathematica

Table[Numerator[n/Sum[1/k^2,{k,1,n}]],{n,1,20}] (* Vaclav Kotesovec, Nov 14 2014 *)

PARI

harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
s=vector(30); for(k=1, #s, s[k]=numerator(harmonicmean(vector(k, i, i^2)))); s