Triangle read by rows: T(n,k) is number of paths from (0,0) to (3n,0) that stay in the first quadrant (but may touch the horizontal axis), consisting of steps u=(2,1),U=(1,2), or d=(1,-1) and have k doubledescents (i.e., dd's).
A108428
Triangle read by rows: T(n,k) is number of paths from (0,0) to (3n,0) that stay in the first quadrant (but may touch the horizontal axis), consisting of steps u=(2,1),U=(1,2), or d=(1,-1) and have k doubledescents (i.e., dd's).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =4a(5) =4a(6) =1a(7) =1a(8) =9a(9) =23a(10) =23a(11) =9a(12) =1a(13) =1a(14) =16a(15) =76a(16) =156a(17) =156a(18) =76a(19) =16a(20) =1a(21) =1a(22) =25a(23) =190a(24) =650a(25) =1167a(26) =1167a(27) =650a(28) =190a(29) =25
External references
- oeis: A108428