ANSWER
C) 1, 3, 6, 10, 15, 21, 28, 36, 45
EXPLANATION
The recursive formula is,
when n is a natural number greater than 1.
When n=2,
when n=3,
when t=4,
When t=5,
when t=6,.
when t=7
When t=8,
When t=9,
Hence the first nine triangular number are
C) 1, 3, 6, 10, 15, 21, 28, 36, 45