Question

11, 15, 31, 67, 131,?

Answer 1

the next number will be 231 
As,
    2,4,6,8,10............
are even numbers 
(2)²=4
first number is 11+4=15 
then (4)²=16
15+16=31
then (6)²=36
31+36=67
then (8)²=64
67+64=131
then (10)²=100 
131+100==231