The pattern is add three and then multiply by three. The next number is 174.
174 =============== 18 = 15+3 54 = 18x3 57 = 54+3 171= 57x3 174= 171+3
171 - 38 = 133 so 133 + 38 sum to 171
15
131 all have odd numbers, so does 151 and 171. i would say 161 is the one that doesn't belong because it has an even number in it.
the next two are 174 and 522.
174 =============== 18 = 15+3 54 = 18x3 57 = 54+3 171= 57x3 174= 171+3
You need at least two numbers to find a GCF.
1, 3, 9, 19, 57, 171.
171 can be divided by each of its factors: 1, 3, 9, 19, 57 and 171
171
171 is not a prime number. These numbers go evenly into 171: 1 3 9 19 57 171.
171 = 171/1 and 109 = 109/1 are fractional representations of the numbers.
The numbers are: (-12+square root of 171) and (-12-square root of 171)
They are members of the infinite set of numbers of the form 171*k where k is an integer.
The multiples of 171 (which are infinite) are all divisible by 171 , including these: 171, 342, 513, 684, 855, 1026, 1197, 1368, 1539 . . .
171 - 38 = 133 so 133 + 38 sum to 171
171