Number of permutations p of (1,2,3,...,n) such that k+p(k) is prime for 1<=k<=n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =1a(5) =9a(6) =4a(7) =36a(8) =36a(9) =676a(10) =400a(11) =9216a(12) =3600a(13) =44100a(14) =36100a(15) =1223236a(16) =583696a(17) =14130081a(18) =5461569a(19) =158180929a(20) =96275344a(21) =5486661184a(22) =2454013444a(23) =179677645456a(24) =108938283364