say "Arithmetic derivative for n in range [-99, 100]:"
-99 .. 100 -> map { .arithmetic_derivative }.each_slice(10, {|*a|
    a.map { '%4s' % _ }.join(' ').say
})

say "\nArithmetic derivative D(10^n)/7 for n in range [1, 20]:"
for n in (1..20) {
    say "D(10^#{n})/7 = #{arithmetic_derivative(10**n) / 7}"
}