> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/sidef-lang/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/sidef-lang/programming_tasks/i/iterated_digits_squaring.md).

# Iterated digits squaring

```ruby
func digit_square_sum_iter(n) is cached {

    if ((n == 1) || (n == 89)) {
        return n
    }

    __FUNC__(n.digits.sum { .sqr })
}

say (1..1e6 -> count_by { digit_square_sum_iter(_) == 89 })
```

## Output:

```
856929
```