# Duffinian numbers

```ruby
func is_duffinian(n) {
    n.is_composite && n.is_coprime(n.sigma)
}
 
say "First 50 Duffinian numbers:"
say 50.by(is_duffinian)
 
say "\nFirst 15 Duffinian triplets:"
15.by{|n| ^3 -> all {|k| is_duffinian(n+k) } }.each {|n|
    printf("(%s, %s, %s)\n", n, n+1, n+2)
}
```

#### Output:

```
First 50 Duffinian numbers:
[4, 8, 9, 16, 21, 25, 27, 32, 35, 36, 39, 49, 50, 55, 57, 63, 64, 65, 75, 77, 81, 85, 93, 98, 100, 111, 115, 119, 121, 125, 128, 129, 133, 143, 144, 155, 161, 169, 171, 175, 183, 185, 187, 189, 201, 203, 205, 209, 215, 217]

First 15 Duffinian triplets:
(63, 64, 65)
(323, 324, 325)
(511, 512, 513)
(721, 722, 723)
(899, 900, 901)
(1443, 1444, 1445)
(2303, 2304, 2305)
(2449, 2450, 2451)
(3599, 3600, 3601)
(3871, 3872, 3873)
(5183, 5184, 5185)
(5617, 5618, 5619)
(6049, 6050, 6051)
(6399, 6400, 6401)
(8449, 8450, 8451)
```


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