Ben Green has shown that the answer is O ( 2 N / 2 ) {\displaystyle O(2^{N/2})} , as predicted by the Cameron–Erdős conjecture (see Sloane's OEIS: A007865).
Ben Green megmutatta, hogy a válasz O ( 2 N / 2 ) {\displaystyle O(2^{N/2})} , ahogy azt a Cameron–Erdős-sejtés megjósolta (lásd Sloane:  A007865).