Number of permutations tau of {1,...,n} such that k^2 + tau(k)^2 is prime for every k = 1,...,n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =4a(6) =0a(7) =16a(8) =4a(9) =144a(10) =64a(11) =81a(12) =256a(13) =5184a(14) =1600a(15) =25600a(16) =8100a(17) =183184a(18) =108900a(19) =5924356a(20) =342225a(21) =9066121a(22) =11356900a(23) =106853569a(24) =105698961a(25) =16119349444a(26) =1419933124a(27) =69792129124a(28) =14251584400a(29) =613950602500