OFFSET
0,4
COMMENTS
w = harmonic mean of {x,y,z,n}. For a guide to related sequences, see A211795.
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[4/w == 1/x + 1/y + 1/z + 1/n, s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 60]] (* A212256 *)
(* Peter J. C. Moses, Apr 13 2012 *)
PROG
(PARI) A212256(n) = sum(w=1, n, sum(x=1, n, sum(y=1, n, sum(z=1, n, (4/w)==((1/x)+(1/y)+(1/z)+(1/n)))))); \\ (Is there any significantly faster program?) - Antti Karttunen, Feb 15 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, May 15 2012
STATUS
approved