The number of down-up permutations of [n] where adjacent elements differ by at least 4.
A249391
The number of down-up permutations of [n] where adjacent elements differ by at least 4.
Terms
- a(0) =1a(1) =1a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =1a(9) =16a(10) =272a(11) =2880a(12) =32648a(13) =333696a(14) =3617545a(15) =38942336a(16) =443291226a(17) =5168682752a(18) =63523977424a(19) =807890646528
External references
- oeis: A249391