28485

Appears in sequences

• Symmetric secondary structures of RNA molecules with n nucleotides.at n=25A088518
• Number of left factors of peakless Motzkin paths of length n.at n=12A091964
• Triangle read by rows: T(n,k) is the number of paths of length n with steps U=(1,1), D=(1,-1) and H=(1,0), starting at (0,0), staying weakly above the x-axis (i.e., left factors of Motzkin paths) and having k peaks (i.e., UDs), 0 <= k <= floor(n/2).at n=42A132893
• Start with a single square; at n-th generation add a square at each expandable vertex (this is the "vertex to side" version); a(n) is the sum of all label values at n-th generation. (See comment for construction rules.)at n=20A247903
• Number of meanders of length n with Dyck-steps avoiding the consecutive steps UDU and DUD.at n=25A329703
• Triangle read by rows, the Riordan square of the number of achiral m-color cyclic compositions of n (A308747). T(n,k) for 1 <= k <= n.at n=32A336452