  In answer to a question of Long, Flapan constructed an example of a prime
strongly positive amphicheiral knot that is not slice. Long had proved that all
such knots are algebraically slice. Here we show that the concordance group of
algebraically slice knots contains an infinitely generated free subgroup that
is generated by prime strongly positive amphicheiral knots. A simple corollary
of this result is the existence of positive amphicheiral knots that are not of
order two in concordance.
