В мире информатики и математики

Задача 1. 

import math

F = [1] * 3000
for n in range(100):
   if n == 1:
       F[n] = 1
   if n == 2:
       F[n] = 2
   if n > 2 and n%2==0:
       F[n] =(3*n + F[n - 3])/3
   if n > 2 and n % 2 != 0:
       F[n] = (7 * n + F[n - 1]-F[n-2])/5
print(math.floor(F[35]))

Задача 2.

F = [1] * 3000
for n in range(100):
   if n == 1:
       F[n] = 1
   if n > 1:
       F[n] =F[n-1]+2**(n-1)

print(F[10])

Задача 3
b=5+6**20
k=0
F = [1]*10000000
for n in range(1,100000):
   if n < 9:
       F[n] = n
   if n>=9:
      F[n]=F[n%9]+F[n//9]
      print(n,F[n])
   if  1<=n<=100000 and F[n]==21:
      k=k+1
print(k)