What is the next number in series 1,3,7,25,103,?

(i) 526

(ii) 521

(iii) 515

(iv) 509

I feel that there is some mistake in the question since...there is no relation between the 4^th and 3^rd, 5^th and 4^th ..

 

Please recheck the question.....

I too feel the same but this question has been given in FIITJEE mental ability book for Udaya-I for class 8. In book its answer has been given as 521 but no logic has been given for it. If anyone can relate any logic to it, it will be great.

1 * 1 + 2 =3

3 * 2 + 1=7

7 * 3 + 4=25

25 * 4 + 3=103

103 * 5 + 6=521

521 * 6 + 5=3131

Here the sequence is first multiply by 2 and then add 1 AND

in the next number the reverse is following .

 

1,3,7,25,103,......

The series can be represented as
1,1+2,3+4,12+13,52+51,260+261

We observe

Third term is second term higher value i.e.(2*1)*2+2*2-1

Fourth term is higher value 4*3+4*3+1

Fifth term is higher value 13*4+13*4-1

Sixth term will be higher value i.e. 52*5+52*5(+or -)1