Question 799232
n = 4, there 4 types of values you can choose from i.e. 3,5,7 or 9
r = 4, of these 4types you must produce a combination that has 4 digits

thus the total number of possible combinations is found using the formula

(n+r-1)!/r!(n-1)!

if and only if repetitions are allowed.

Combinations with repetition (n=4, r=4)

35 entries.
{3,3,3,3} {3,3,3,5} {3,3,3,7} {3,3,3,9} {3,3,5,5} {3,3,5,7} {3,3,5,9} {3,3,7,7} {3,3,7,9} {3,3,9,9} {3,5,5,5} {3,5,5,7} {3,5,5,9} {3,5,7,7} {3,5,7,9} {3,5,9,9} {3,7,7,7} {3,7,7,9} {3,7,9,9} {3,9,9,9} {5,5,5,5} {5,5,5,7} {5,5,5,9} {5,5,7,7} {5,5,7,9} {5,5,9,9} {5,7,7,7} {5,7,7,9} {5,7,9,9} {5,9,9,9} {7,7,7,7} {7,7,7,9} {7,7,9,9} {7,9,9,9} {9,9,9,9}