main.raku

use Test;

is disarium-numbers(19),
   [ 0,1,2,3,4,5,6,7,8,9,89,135,175,518,598,1306,1676,2427,2646798 ];

done-testing;

sub is-disarium-number(Int $n where $n >= 0 --> Bool) {
    $n == ^($n.chars)
        .map({
            $n.substr( $_, 1 ) ** ( $_ + 1 )
        })
        .sum
}

sub disarium-numbers(Int $n where $n > 0) {
    (^Inf).hyper.grep({ .&is-disarium-number }).head: $n
}