Illustrates using built-in Ruby counter to present numbers as upper case strings including 'A' - 'Z'.

alpha_counter.txt

2.5.1 :022 > def fmt(n); n.to_s(26).chars.map { |c| (c.ord + 16).chr }.join; end
 => :fmt
2.5.1 :023 > def val(s); s.chars.map { |c| (c.ord - 16).chr }.join.to_i(26); end
 => :val
2.5.1 :024 > n = (26 * 26) + (2 * 26) + 3  # 'ABC'
 => 731
2.5.1 :025 > fmt n
 => "ABC"
2.5.1 :026 > val 'ABC'
 => 731