**11) 1, 2, 5, ?, 677**

**Answer**: 26

**Explanation**: 1, 1^{2} + 1, 2^{2} + 1, 5^{2} + 1= 26, 26^{2} + 1

**12) 2, 11, 56, 281, ?**

**Answer**: 1406

**Explanation**: 2, 2*5+1=11, 11*5+1=56, 56*5+1=281, 281*5+1=1406

**13) 2, 10, 26, 50, 82, ?**

**Answer**: 122

**Explanation**: 1^{2}+1, 3^{2}+1, 5^{2}+1, 7^{2}+1, 9^{2}+1, 11^{2}+1

**14) 3, 4, 7, 7, 13, 13, 21, 22, 31, 34, ?**

**Answer**: 43

**Explanation**: pattern 1 I. 3, 7, 13, 21, 31, ? and pattern 2 4, 7, 13, 22, 34, So, 31 + 12 = 43

**15) 198, 194, 185, 169, ?**

**Answer**: 144

**Explanation**:- 22, – 32, – 42,….. So, 169 – 52 = 169 – 25 = 144

**16) 2, 3, 5,7,11,?, 17**

**Answer**: 13

**Explanation**: prime numbers

**17) 6, 12, 21, ?, 48**

**Answer**: 33

**Explanation**: + 6, + 9, + 12, + 15, ….. So, 21 + 12 = 33

**18) Which term of the series 5, 10, 20, 40, ….. is 1280?**

**Answer**: 9th

**Explanation**: 5 x 2 = 10, 10 x 2 = 20, 20 x 2 = 40,….., a = 5 and r = 2. -> 5×2^{(9)-1 }= 1280

**19) 2, 5, 9, ?, 20, 27**

**Answer**: 14

**Explanation**: + 3, + 4, + 5, + 6,….. So, 9 + 5 = 14

**20) 2, 3, 3, 5, 10, 13, ?, 43, 172, 177**

**Answer**: 39

**Explanation**:+ 1, x 1, + 2, x 2, + 3, x 3, + 4, x 4, + 5 So, 13 x 3 = 39