Задача 1:
N = int(input())
S = 0
chislo = 0
while chislo!=2*N:
    S += chislo * (chislo+1)
    chislo+=1
    print(chislo,S)
print(S)

Задача 2: 
N = int(input())
S = 0
chislo = 0
while chislo!=N:
    chislo+=1
    S += (chislo+1)/chislo
print(S)

Задача 3: 
N = int(input())
S = 1
chislo = 0
while chislo!=2*N:
    chislo+=2
    S *= chislo
print(S)