**Given:** a_{n} = 1 – 4n

**Taking n = 1,**

a_{1} = 1 – 4(1) = 1 – 4 = -3

**Taking n = 2,**

a_{2} = 1 – 4(2) = 1 – 8 = -7

**Taking n = 3,**

a_{3} = 1 – 4(3) = 1 – 12 = -11

Therefore the series is -3, -7, -11, …

So, a = -3, d = a_{2} – a_{1} = -7 – (-3) = -7 + 3 = -4

Now, we have to find the sum of the first 25 terms of the AP

⇒ S_{25} = 25 × (-51)

⇒ S_{25} = -1275

**Hence, the sum of 25 terms is -1275.**