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The least prime $p$ such that $p+2n$ is also prime: A020483$(n)$, and the smallest number $x$ such that $\sigma(x+2n) = \sigma(x)+2n$: A054906$(n)$.

The smallest prime in which a digit appears $n$ times: A084673$(n)$, and the smallest prime containing exactly $n$ $1$'s: A037055$(n)$, for $n>1$.

The number of subwords of length $n$ in the infinite word generated by $a \to aab, \ b \to b$ : A006697$(n)$, and the maximal number of distinct nonempty substrings of any binary string of length $n$, plus one: A094913$(n)+1$.

The number of distinct values taken by ${\omega}$^${\omega}$^${\dots}$^${\omega}$ (with $n$ $\omega$'s and parentheses inserted in all possible ways) where $\omega$ is the first transfinite ordinal omega: A199812$(n)$, and the number of unlabeled rooted trees with at most $n$ nodes A087803$(n)$, minus $n$ plus one: A255170$(n)$.

The number of transitive permutation groups of degree $n$: A002106$(n)$ is conjectured to be the number of Galois groups for irreducible polynomials (over $\mathbb{Q}$) of order $n$ (such groups are transitive). It is a particular case of the Inverse Galois problem.