# 3s nd 9s

**Number Theory**Level 3

A number n is such that 3n and n both have the same sum of digits. (Sum of digits means 17 has 1+7=8 as its sum of digits). n is a natural number. Then:

A. 3n is a multiple of 9

B. n is a multiple of 3

C. n is a multiple of 9

D. 3n is a multiple of 81.

E. 3n is a multiple of 3

Which of the above are DEFINITELY true?