> 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/l/luhn_test_of_credit_card_numbers.md).

# Luhn test of credit card numbers

```ruby
func luhn (n) {
    static a = {|j| (2*j // 10) + (2*j % 10) }.map(^10)

    var checksum = n.digits.map_kv {|i,j|
        i.is_odd ? a[j] : j
    }.sum

    checksum % 10 == 0
}

for n in [49927398716, 49927398717, 1234567812345678, 1234567812345670] {
    say [n, luhn(n)]
}
```

#### Output:

```
[49927398716, true]
[49927398717, false]
[1234567812345678, false]
[1234567812345670, true]
```