Regular expression to find words and digits that are repeated back to back

Suppose I have a data frame

```
df<-data.frame(name=c("mike","mike","mike","bob","mike"),age=c(23,23,23,25,23)

```

how can I write a regular expression to check "name" column whether "mike" or any other word is repeated back to bake for e.g here mike is repeated 3 times and in "age" column a digit is repeated e.g here 23 is repeated 3 times back to back