# sum the digits of a number
def sum_digits (n):
  sum_num = 0
  while (n > 0):
    sum_num += (n % 10)
    n = n // 10
  return sum_num

# reverse a number
def rev_num (n):
  rev_n = 0
  while (n > 0):
    rev_n = rev_n * 10 + (n % 10)
    n = n // 10
  return rev_n

# determine if a number is palindromic
def is_palindromic (n):
  return (n == rev_num(n))
   
# sum the proper divisors of a number
def sum_divisors (n):
  sum_div = 0
  limit = n // 2
  div = 1
  while (div <= limit):
    if (n % div == 0):
      sum_div += div
    div += 1
  return sum_div

# determine if a number is prime
def is_prime (n):
  if (n == 1):
    return False
  limit = int (n ** 0.5) + 1
  div = 2
  while (div < limit):
    if (n % div == 0):
      return False
    div += 1
  return True

def main():
  # prompt the user to enter a number
  num = int (input ("Enter a number: "))

  # print the sum of the digits
  print (sum_digits (num))
  print ()

  # print the reverse of a number
  print (rev_num (num))
  print ()

  # print all perfect numbers less than 10000
  n = 1
  while (n <= 10000):
    if (n == sum_divisors (n)):
      print (n)
    n += 1
  print ()

  # find 4 digit non-palindromic number whose cube is palindromic
  for n in range (1000, 10000):
    if (not is_palindromic (n) and is_palindromic (n * n * n)):
      print (n)
      break
  print ()

  # print all prime numbers less than equal to 50
  for i in range (1, 51):
    if (is_prime(i)):
      print (i)
  print ()

  # find all 3-digit emirps
  for n in range (100, 1000):
    cond1 = not (is_palindromic (n)) and is_prime (n)
    cond2 = is_prime (rev_num(n))
    if (cond1 and cond2):
      print (n)
  print()

  # find all twin primes less than 100
  for n in range (2, 100):
    if (is_prime (n) and is_prime (n + 2)):
      n2 = n + 2
      print (n, n2)
  print ()


main()