Challenging Number Pattern?

Study the number pattern.

1, 3. 5, 3, 5, 7, 5, 7, 9, 7, 9, 11

(a) At what position does the first 15 appear?
(b) Find the value of the 27th number.
(c) Find the sum of the first 30 numbers.


Answers:
1,3,5,3,5,7,5,7,9,7,9,11,9,11,13,11,13,15,13,15,17,15,17,19,17,19,21...
(a)  18th Position
(b) 21
(c) 360