### Brain Teasers

# 2, 6, 15, 28, ?, 78

Find the missing number in the following series:

2, 6, 15, 28, ?, 78

2, 6, 15, 28, ?, 78

### Answer

55First take 1 multiplied by the first prime number (2), 2 * second prime number (3), 3 * third prime number (5) and so on.

Therefore the answer is 5 * 11 = 55.

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## Comments

Okay...Did you do something wrong or is it just me? Let me show you...2 (2*3),6 (3*5), 15, then (5*7)=35. Did you forget about seven (7)? The series should go as follows: 2, 6, 15, 35, 77, 143, right?

Maybe this will help to explain it: 1 multiplied by the 1st prime number, 2 multiplied by the 2nd prime, 3 by the 3rd, 4 by the 4th...

Good teaser. And the next number would be 7x17=119, right?

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