OFFSET
1,1
COMMENTS
EXAMPLE
The third quadruple is 12, 60, 128, 160, hence a(3) = gcd(4*3,4*3*5,4*32,4*8*5) = 4.
PROG
(PARI) {m=1760; for(n=6, m, for(a=1, (n-3)\3, for(b=a+1, (n-a-1)\2, c=n-a-b; d=a*b*c%(a+b+c); if(c<d, if(a*b*d%(a+b+d) == c, if(a*c*d%(a+c+d) == b, if(b*c*d%(b+c+d) == a, print1(gcd(a, gcd(b, gcd(c, d))), ", "))))))))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Klaus Brockhaus, Mar 12 2004
STATUS
approved