progression.py

# Arithmetic progression

# Input
# Second task : calculate sum of ai

debug = True
allow_input = False if debug else True

if allow_input:
    n=int(input("Input n: "))
    a1=int(input("Input a1: "))
    d=int(input("Input d: "))
else:
    n = 20
    a1 = 1
    d=10

i=1
a=a1

while i<n:
    a=a+d
    i=i+1

if debug:
    # Check our algorithm
    b = a1+(n-1)*d
    assert b == a

# Output
print('Memeber number', n, 'of the progression is', a)