m = 5;

N = 20;

sum1 = 1;
sum2 = 1;
for i=1:N
  sum1 = sum1 + (-m)^i/factorial(i);
end
for i=1:N
  sum2 = sum2 + (m)^i/factorial(i);
end

sum1
sum2 = 1/sum2
exp(-m)

% digit
% mm = vpa(5);
% sum