Esthetic numbers

func generate_esthetic(root, upto, callback, b=10) {

    var v = root.digits2num(b)

    return nil if (v > upto)
    callback(v)

    var t = root.head

    __FUNC__([t+1, root...], upto, callback, b) if (t+1  < b)
    __FUNC__([t-1, root...], upto, callback, b) if (t-1 >= 0)
}

func between_esthetic(from, upto, b=10) {
    gather {
        for k in (1..^b) {
            generate_esthetic([k], upto, { take(_) if (_ >= from) }, b)
        }
    }.sort
}

func first_n_esthetic(n, b=10) {
    for (var m = n**2; true ; m *= b) {
        var list = between_esthetic(1, m, b)
        return list.first(n) if (list.len >= n)
    }
}

for b in (2..16) {
    say "\n#{b}-esthetic numbers with indices #{4*b}..#{6*b}: "
    say first_n_esthetic(6*b, b).last(6*b - 4*b + 1).map{.base(b)}.join(' ')
}

say "\nBase 10 esthetic numbers between 1,000 and 9,999:"
between_esthetic(1e3, 1e4).slices(20).each { .join(' ').say }

say "\nBase 10 esthetic numbers between 100,000,000 and 130,000,000:"
between_esthetic(1e8, 13e7).slices(9).each { .join(' ').say }

Output:

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