The answer will depend on where in the sequence the missing number is:
Using only quartic polynomials, the solutions are:
3, 10, 25, 54, 103
10, 11.75, 25, 54, 103
10, 25, 33.8333..., 54, 103
10, 25, 54, 84.25, 103
10, 25, 54, 103, 178.
Other functional forms will generate many more answers.
The missing number is 26. The number after 29 is 58.
17-12n 17-12(10)=-103
c) 17
It is7
14
178 is the answer By using the formula a{n} = n³ + n² + 5n + 3 For e.g. A{2} =2 ³ +2²+5*2+3=25 =8+4+10+3=25 And so on.    = 10, 25, 54, 103, 178
The missing number is 26. The number after 29 is 58.
7 6,7,8,9,10
Dodging numbers may be missing numbers in a sequence. For example, the underscore in the following sequence represents such a number: 2, 4, _ , 8, 10.
342
356
17-12n 17-12(10)=-103
If the question is, What is the missing number in the sequence 7, 11, 23, ?, 167? Then each number is 3 times the previous number then deduct 10. 3 x 7 = 21 - 10 = 11 3 x 11= 33 - 10 = 23 3 x 23 = 69 - 10 = 59......the missing number 3 x 59 = 177 - 10 = 167 3 x 167 = 501 - 10 = 491....the next number in the sequence.
16
10 (between 7 and 13)
c) 17
It is7