Project Euler problem#15

#python program to find the lattice path of 20x20 grid a=[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1] for j in range(1,21): i=1 while i <21 : a[i] = int(a[i-1])+int(a[i]) i+=1 print (a[20])