The larger numbers are multiples of the smaller numbers before and after.
... 4 20 5 30 6 42 7 56 ...
4 x 5 = 20
5 x 6 = 30
6 x 7 = 42
7 x 8 = 56 You can say it another way with division: 4 into 20 is 5, 5 into 30 is 6, 6 into 42 is 7, 7 into 56 is 8... (I just added the 4 and the 56 into the sequence to make the pattern easier to see. You can extend it in both directions.)
The next number in the sequence will be 56.
54
12+5 = 6 22+5 = 9 32+5 = 14 42+5 = 21 52+5 = 30 62+5 = 41 Square the sequence number then add 5.
35
5
56
The number which best completes the sequence below is 20 5 30 6 42 7
The next number in the sequence will be 56.
56
56
20 5 30 6 42 7 56 8............... 4*5=20 5*6=30 6*7=42 7*8=56
54
56
56, 8.
56, 8, 72, 9
56
56 (just the next number, not the number that completes the sequence)