5531 5506 5425 5304 5135 4910 4621
May be this question is to identify the wrong number in the series...
5531 – 5506: 25 <-- 5^2 (Series should have started with a difference of 49 ( 7^2) and hence 5555)
5506 – 5425: 81 <-- 9^2
5425 – 5304: 121 <-- 11^2
5304 – 5135: 169 <-- 13^2
5135 – 4910: 225 <-- 15^2
4910 – 4621: 289 <-- 17^2
So, the wrong number is: 5531
Option: 1