Irregular triangle read by rows: T(n,k) = number of size k subsets of S_n that remain unchanged by a rotation of 180 degrees.
A277083
Irregular triangle read by rows: T(n,k) = number of size k subsets of S_n that remain unchanged by a rotation of 180 degrees.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =1a(7) =1a(8) =2a(9) =3a(10) =4a(11) =3a(12) =2a(13) =1a(14) =1a(15) =8a(16) =36a(17) =120a(18) =322a(19) =728a(20) =1428a(21) =2472a(22) =3823a(23) =5328a(24) =6728a(25) =7728a(26) =8092a(27) =7728a(28) =6728a(29) =5328
External references
- oeis: A277083