Chowla Numbers

Write a script to generate first 20 Chowla Numbers, named after, Sarvadaman D. S. Chowla, a London born Indian American mathematician. It is defined as:
C(n) = (sum of divisors of n) - 1 - n

proc chowla {n} {
    set sum 0
    for {set i 2} {[expr $i * $i] <= $n} {incr i} {
        if {[expr $n % $i]==0} {
            set sum [expr $sum + $i]
            set j [expr int($n / $i)]
            if {$j != $i} {
                set sum [expr $sum + $j]
            }
        }
    }

    return $sum
}

for {set i 1} {$i <= 20} {incr i} {
    puts "chowla($i) = [chowla $i]"
}