Number of permutations p on the set [n] with the properties that abs(p(i)-i) <= 3 for all i, p(1) <= 2, and p(4) >= 2.
A188495
Number of permutations p on the set [n] with the properties that abs(p(i)-i) <= 3 for all i, p(1) <= 2, and p(4) >= 2.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =4a(4) =10a(5) =36a(6) =120a(7) =368a(8) =1089a(9) =3304a(10) =10168a(11) =31312a(12) =95880a(13) =293120a(14) =896824a(15) =2746569a(16) =8411818a(17) =25756220a(18) =78853410a(19) =241421436a(20) =739183568a(21) =2263249600a(22) =6929580817a(23) =21216729488a(24) =64960656448a(25) =198894856144a(26) =608971496032
External references
- oeis: A188495