Question 1210225
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The last given number in the sequence is {{{13=3^0+3^1+3^2}}}.<br>
Since that number is the sum of all the distinct powers of 3 up to the second power, the next number in the sequence must involve the third power of 3.<br>
3 to the third power is 27, which is greater than 20, so it is the next number in the sequence.<br>
ANSWER: 27<br>