Set of integers that all pairwise sums are semiprimes? E.g., s = {1,3,32,54} with pairwise sums 4,33,55, 35,57, 86 all semiprimes Set of integers that all pairwise differences are semiprimes? E.g., s={ 1, 5, 11, 15, 134, 220} with pairwise differences 4,10,14,133,221, 6,10,129,215, 4,123,209 119,205 86 all semiprimes. -- Zak Seidov