Consider three distinct integers a,b,c such that all 4 numbers a+b+c, a+b-c, a-b+c and -a+b+c are positive/negative primes. E.g., for a=3 and b=4, c = 12,30,60,270,570,600,1230,1290,1620,2340,2550,3540,4020,4650,5850,6270,6360,6570,.... Is this problem the old hat? What can be said about c in this particular case? -- Zak Seidov