Python program for arthmetic progression (A.P)

ap.py

# Ask for First term and Common difference
a = eval(input("\nEnter First Term: "))
d = eval(input("Enter Common difference: "))

# Extend the range to greater upper bound
for i in range(20000000000000000000000):

    # Ask for nth term 
    n = eval(input("\nEnter nth term: "))

    # Apply formula
    Tn = a + ((n - 1) * d)

    # Print Answer
    print("\n------------------------------\nnth Term of the sequence: ", Tn, "\n------------------------------\n")

    # Keep prompting till valid input
    while (True):
        ask = input("Do you want to continue? (Y / N)\nType Option: ")

        if ask.upper() == "N":
            print("\nThankyou!\n")
            exit(0)

        if ask.upper() == "Y":
            break

        if ask.upper() != "Y" and ask.upper() != "N":
            print("Please Enter Correct Input\n")