A sequence is defined as shown for n = 3, 4, 5, ... What will be the first number in this sequence that is NOT prime?
a_1 = 11
a_2 = 2
a_3 = a_2 + a_1
a_4 = a_3 + a_2 + 2
a_5 = a_4 + a_3 + 4
...
a_{n + 1} = a_n + a_{n - 1} + 2(n - 2)
a3 = 13
a4 = 17
a5 = 34 not prime
