An equivalence relation on permutations.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =17a(5) =67a(6) =352a(7) =1969a(8) =13295a(9) =97619a(10) =848354a(11) =7647499a(12) =82862683a(13) =897904165a(14) =11226063188a(15) =146116260203