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%I #18 Sep 08 2021 00:58:04
%S 6,71,272,586,978,1591,1865,3115,3772,4964,4225,8433,4987,10667,13659,
%T 10845,7513,17360,9569,28554,23309,17220,12326,37554,19984,24091,
%U 31056,42343,16095,57001,15076,42655,46885,38416,77887,71959,16692,42054,68894,95914,24566,100023,24224,99437,108756,41907,29711,127069,52811,94745,83433
%N Number of ways 1/n can be expressed as the sum of four distinct unit fractions: 1/n = 1/w + 1/x + 1/y + 1/z satisfying 0 < w < x < y < z.
%H Jud McCranie, <a href="/A241883/b241883.txt">Table of n, a(n) for n = 1..644</a>
%e 1/1 = 1/2 + 1/3 + 1/7 + 1/42
%e = 1/2 + 1/3 + 1/8 + 1/24
%e = 1/2 + 1/3 + 1/9 + 1/18
%e = 1/2 + 1/3 + 1/10 + 1/15
%e = 1/2 + 1/4 + 1/5 + 1/20
%e = 1/2 + 1/4 + 1/6 + 1/12
%e so a(1) = 6.
%t a[n_] := Length@ Solve[1/n == 1/w + 1/x + 1/y + 1/z && 0 < w < x < y < z, {w, x, y, z}, Integers]; Array[f, 21]
%Y Cf. A002966, A004194, A020327, A227610.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Apr 30 2014