The answer depends on where the missing number is meant to be.
If 2, 4, 6, 10, 26, X: then X = 72
If 2, 4, 6, 10, X, 26: then X = 16.8
If 2, 4, 6, X, 10, 26: then X = 6.6
If 2, 4, X, 6, 10, 26: then X = 5.4
If 2, X, 4, 6, 10, 26: then X = 1.2
If X, 2, 4, 6, 10, 26: then X = 6
17. The numbers are being increased by odd numbers beginning with 3.
26
26. The sequence can be seen either as decreasing multiples of 13 or, more generally, 65 - 13n where n = 1, 2, 3, ...
20, 21, 22, 23, 24, 25, 26, 27, 28, 29
42, each number in the sequence is the addition of the previous two: 2-2-4-6-10-16-26 2+2=4 4+6=10 6+10=16 10+16=26 16+26=42
The missing number is 26. The number after 29 is 58.
There does not appear to be a missing number. The sequence is n2 + 1. 12 + 1 = 2 : 22 + 1 = 5 : 52 + 1 = 26 : 262 + 1 = 677. The next number in the sequence is 6772 + 1 = 458330.
26 As far as I can tell the sequence is +10,-5,+10,-5.
17. The numbers are being increased by odd numbers beginning with 3.
If these are the only numbers give, then: 2, 10, 26 = 2 (+8), 10 (+16), 26 (+32), 58 (+64), 122... the amount being increased keeps doubling....the sequence would read: 2, 10, 26, 58, 122...
26
58
assuming it keeps the same pattern of +10 -5 alternating then the next number would be 26
29
26
20, 21, 22, 23, 24, 25, 26, 27, 28, 29
26. The sequence can be seen either as decreasing multiples of 13 or, more generally, 65 - 13n where n = 1, 2, 3, ...