1x2=2, 2x2=4, 4x2=8, what's it called? How enter on calculator?

Question

1x2=2, 2x2=4, 4x2=8, what's it called? How enter on calculator?

Answer 1

This is a geometric sequence, with a₁ = 1 and common ratio = 2.

 

The formula for a geometric sequence is: a_n = a₁*r^n-1

 

If you want the nth term, you would use the formula above.  For example if you wanted the 10th term:

a₁₀ = 1*2^10-1 = 1*2⁹ = 512