Number of permutations of [n] having no isolated entries. An entry j of a permutation p is isolated if it is not preceded by j-1 and not followed by j+1. For example, the permutation 23178564 has 2 isolated entries: 1 and 4.
A180564
Number of permutations of [n] having no isolated entries. An entry j of a permutation p is isolated if it is not preceded by j-1 and not followed by j+1. For example, the permutation 23178564 has 2 isolated entries: 1 and 4.
Terms
- a(0) =1a(1) =0a(2) =1a(3) =1a(4) =2a(5) =3a(6) =7a(7) =14a(8) =35a(9) =81a(10) =216a(11) =557a(12) =1583a(13) =4444a(14) =13389a(15) =40313a(16) =128110a(17) =409519a(18) =1366479a(19) =4603338a(20) =16064047a(21) =56708713a(22) =206238116a(23) =759535545a(24) =2870002519a(25) =10986716984a(26) =43019064953a(27) =170663829777a(28) =690840124506
External references
- oeis: A180564