Number of down-up permutations of n+4 starting with 4.
A006216
Number of down-up permutations of n+4 starting with 4.
Terms
- a(0) =2a(1) =5a(2) =14a(3) =46a(4) =178a(5) =800a(6) =4094a(7) =23536a(8) =150178a(9) =1053440a(10) =8057774a(11) =66750976a(12) =595380178a(13) =5688903680a(14) =57975175454a(15) =627692271616
External references
- oeis: A006216