18.
1+3=4
3+4=7
4+7=11
7+11=18
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-27 You subtract powers of 2 everytime... 1,2,4,8,16
42 as you have to add the next prime number onto the previous value.
42 is the next number in this sequence. This number sequence is adding the next prime number to the last number. So 1 + 2 = 3. Then 3 + 3 = 6, 6 + 5 = 11, 11 + 7 = 18, 18 + 11 = 29. The next prime number after 11 is 13, so 29 + 13 = 42. The next numbers would be 59 (42+17), 78 (59+19), and 101 (78+23)
It is: 47 because 18+29 = 47
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