Counting binary trees
44454
Rooted Binary Trees and Catalan Numbers
101642
Counting in a rectangular grid with obstacles
44304
Number of labeled trees which have one vertex of degree 4
85104
Counting train stops using combinatorics
95755
Counting the population of integers
27273
Count the number of topological sorts for poset (A|)?
98355
Is the set of all possible binary strings countable?
24212
proving how many permutations exist.
143427
Counting existing permutations in R
144821
Number of ordered pairs of subsets
134599
How do I do Combinatorics / Counting?
100256
Proof by induction on a rooted tree with even number of vertices
106255
How do I make an unbalanced binary tree?
48838
Proving the number of $n$ length binary strings with no consecutive $1's$ $b_n$ is equal to $b_{n-1} + b_{n-2}$
99931
Number of connected graphs on labeled vertices, counted according to parity
142809
Trees whose complement is also a tree
52348
Counting the number of surjections.