experimental-projects/oeis-research/Falcon Shapiro/Smallest number that requires at least n distinct repdigits to sum/prog.sf

#!/usr/bin/ruby

# a(n) is the smallest number that requires at least n distinct repdigits to sum.
# https://oeis.org/A336759

# Known terms:
#   1, 10, 21, 309, 2108, 21996

var n = 5
var limit = 21996

var arr = []

for k in (1..9) {
    for j in (1..limit.len) {
        arr << Num("#{k}"*j)
    }
}

arr = arr.grep { _ < limit }.uniq.sort

var seen = Hash()

for k in (1..n) {
    arr.combinations(k, {|*a|
        var t = a.sum

        if (seen.has(t)) {
            seen{t} = k if (k < seen{t})
        }
        else {
            seen{t} = k
        }
    })
}

var z = seen.grep_v{ _ == n }.keys.map{.to_n}.min

say [z, seen{z}]