Good to Solve INMO problem

We can represent any number in the sequence by the differences between digits. For example, 877550 could be represented as (1,0,2,0,5,0). The sum of these is equal to the 1st digit. Then for a given 1st digit, it's a simple matter of stars and bars to find how many numbers in the sequence starting with that digit. 6C5+7C5+...+12C5=1715, and adding 8C5 would bring us above 2005, so the 1st digit must be 8. And we repeat this for subsequent digits.

A CS Solution:

def isnonincreasing(n):
    if int(str(n)[0])>=int(str(n)[1]) and int(str(n)[1])>=int(str(n)[2]) and int(str(n)[2])>=int(str(n)[3]) and int(str(n)[3])>=int(str(n)[4]) and int(str(n)[4])>=int(str(n)[5]):
        return True
    else:
        return False
l=[]
for i in range(100000,1000000):
    if isnonincreasing(i)==True:
        l.append(i)
    else:
        pass
print (l[2004])