In the sequence of 3,5,7,11,17,19,23,25, there is a "different" number?

In the sequence of 3,5,7,11,17,19,23,25, there is a "different" number?

twenty-five
Everything else is prime

For sequence: "1 / (2 ^ n - 1)" sum, Sn =?
It seems that the solution of the second floor can not be eliminated after it is unfolded
Note: the denominator is the n-th power of 2 minus one instead of the n-th power of 2 minus one

Let Sn = a1 + A2 + a3 + an 2Sn=2a1+2a2+2a3…… 2An and 2A1 = A2, 2A2 = A3
And so on, 2an-1 = an  2Sn Sn = 2an-a1, so Sn = (1 / 2 ^ n) - 1

In the sequence 3, 5, 7, 11, 19, 23, 25, there is a number different, it is () a.19 b.13 c.25 d.11

In the sequence 3, 5, 7, 11, 19, 23, 25, there is a number different, it is (C25) a.19 b.13 c.25 d.11
25 is a composite number and the rest are prime numbers

Find the law 1, 7, 19, 35, 59, 89?

an=3n^2-3n+1