How many words with $N$-characters can be formed from the numbers $\{0, 1, 2\}$, such that adjacent numbers have maximum difference 1?
11998
In how many sequences of length $n$, the difference between every 2 adjacent elements is $1$ or $-1$?
153302
$9$ divides $n-r(n)$ where $r(n)$ is $n$ with its digits reversed
24582
Is the set of sequences of natural numbers with trailing zeros countable?
76725
Finding all length-n words on an alphabet that have a specified number of each letter
101719
Finding the n-th lexicographic permutation of a string
127426
Greatest number in the sequence
151466
Series of consecutive numbers (different lengths)
40970
All the ternary n-words with an even sum of digits and a zero.
87664
Combination of $n$ letter out of $3n$.
137573
How many different numbers can you make with the following digits?
22274
Partitioning a natural number $n$ in order to get the maximum product sequence of its addends
74839
Catalan numbers: bijection between applications of a binary operator and Dyck words.
150324
Pigeonhole principle: prove that any set of $n+1$ integers from $\{1,2,...,2n\}$ has two consecutive integers differ by one.
21612
How to prove this form of $n$?
96260
Number of occurrences of k consecutive 1's in a binary string of length n (containing only 1's and 0's)
6204
How many permutations of $\{1, \ldots, n\}$ exist such that none of them contain $(i, i+1)$ (as a sequence) for $i \in {1,...,(n-1)}$?
34452
In how many ways can you choose $k$ numbers out of $\{1,2,3,\dots,n\}$ so none of them is consecutive?