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

A103687

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

Terms

    a(0) =1a(1) =1a(2) =2a(3) =2a(4) =3a(5) =6a(6) =12a(7) =36a(8) =156a(9) =520a(10) =1920a(11) =5760a(12) =12600a(13) =39900a(14) =210140a(15) =844984a(16) =2871876a(17) =8784783a(18) =29392449a(19) =123405524a(20) =726794464a(21) =3669378736a(22) =20998365592a(23) =139906305272a(24) =770298602024

External references