My question: what a formula for finding the number of numbers no greater than n that are divisible by all their suffixes. e.g: 5, 25, 125, 0125, 70125 are divisors of 70125. refinement: $\overline{0...0a_1a_2...} = \overline{a_1a_2...}$

I suggest to rename the tag divisors in a way which distinguishes it more clearly from divisors-multiples. The tag-info for divisors (revision history) clearly says: For questions related to divisors in the sense of algebraic geometry (Cartier divisors, Weil divisors and so on). For question...

A few names are used in different subjects in mathematics with completely distinct meanings. A couple of common examples are "spectrum" and "regular". Sometimes, this creates problems with tags on MathOverflow, as is explained in some of the answers to the question Help cleanup tags!. Specificall...

I want to start out by giving two examples: 1) Graham's problem is to decide whether a given edge-coloring (with two colors) of the complete graph on vertices $\lbrace-1,+1\rbrace^n$ contains a planar $K_4$ colored with just one color. Graham's result is that such a $K_4$ exists provided $n$ is ...

Let $L|K$ be a finite separable extension. Denote the algebraic closure of $K$ by $\bar K$. $\forall x\in L$, denote $d=[L:K(x)]$ and $m=[K(x):K]$. How to show the set $\operatorname{Hom}_K(L,\bar{K})$ of all $K$-embeddings of $L$ is partitioned by the equivalence relation $$\sigma\sim \tau \L...