Number of permutations sigma of {1,2,...,n} such that sigma(i) divides i or i divides sigma(i) for 1 <= i <= n.

A320843

Number of permutations sigma of {1,2,...,n} such that sigma(i) divides i or i divides sigma(i) for 1 <= i <= n.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =3a(4) =8a(5) =10a(6) =36a(7) =41a(8) =132a(9) =250a(10) =700a(11) =750a(12) =4010a(13) =4237a(14) =10680a(15) =24679a(16) =87328a(17) =90478a(18) =435812a(19) =449586a(20) =1939684a(21) =3853278a(22) =8650900a(23) =8840110a(24) =60035322a(25) =80605209a(26) =177211024a(27) =368759752a(28) =1380348224a(29) =1401414640

External references