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(j) >= 2 for j=3,4.
A188498
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(j) >= 2 for j=3,4.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =3a(4) =8a(5) =30a(6) =102a(7) =308a(8) =905a(9) =2744a(10) =8473a(11) =26112a(12) =79924a(13) =244204a(14) =747160a(15) =2288521a(16) =7009458a(17) =21461803a(18) =65704200a(19) =201162258a(20) =615922714a(21) =1885853660a(22) =5774072225a(23) =17678809840a(24) =54128358209a(25) =165728860112a(26) =507424764216
External references
- oeis: A188498