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%I #8 Jan 30 2014 10:34:14
%S 2,3,4,5,6,7,8,9,10,12,15,18,20,24,42
%N Possible values for positive integers a,b,c,d such that 1/a + 1/b + 1/c + 1/d = 1.
%C See A236681 and the link for further motivation.
%H J. Baez, <a href="http://www.math.ucr.edu/home/baez/42.html">42</a>, May 25, 2013.
%e The solutions [a,b,c,d] of 1/a + 1/b + 1/c + 1/d = 1 are, in lexicographical order: {[2, 3, 7, 42], [2, 3, 8, 24], [2, 3, 9, 18], [2, 3, 10, 15], [2, 3, 12, 12], [2, 4, 5, 20], [2, 4, 6, 12], [2, 4, 8, 8], [2, 5, 5, 10], [2, 6, 6, 6], [3, 3, 4, 12], [3, 3, 6, 6], [3, 4, 4, 6], [4, 4, 4, 4]}.
%o (PARI) a=[];forvec(v=vector(3,i,[2,99]),numerator(s=sum(j=1,3,1/v[j],-1))==-1&&a=setunion(a,Set(v)),1);a
%o (PARI) /* to display the solutions */ forvec(v=vector(3,i,[2,99]), numerator(s=sum(j=1,3,1/v[j],-1))==-1&&-1/s>=v[3]&&print1(concat(v,-1/s),", "),1)
%Y Cf. A236681, A236682, A236683, A236684.
%K nonn,fini,full
%O 1,1
%A _M. F. Hasler_, Jan 29 2014
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