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What is the next number in this sequence 7 21 8 72 9

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4 Answers

I guess the answer is 729.
 
Series is 7 21 8 72 9
showing 7*3= 21
8*3^2=8*9=72
Following this series next number could be 9*9^2=9*81=729
 
another pattern could be
7*3=21
8*3^2=72
9*3^3=243
 
One possible pattern is that the odd-numbered terms  are 7, 8, 9, 10, 11, ... and the even numbered terms are 7*3, 7*3^2, 7*3^3,...
Given this pattern the next term is 189

Comments

However, 7*3^2=63 , not 72. A possibility for the even-numbered terms is 3*7, (3^2)*8, (3^3)*9=243,...