When i turned it from i=i+1 into i+=i+1..its showing output 1,3,finished..previously output was 1,2,3,4,5,finished..why?

Question

i = 1
while i <=5:
print(i)
i += i + 1

print("Finished!")

Answer 1

Because i=i+1 in short is writen by i+=1 not as you had writen i+=i+1

i+=i+1 simply means i=i+i+1

Answer 2

Why i+i+1 results 1,3