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efi107
Apr 28, 2009, 11:01 PM
What is the next number in this series?

1 , 2 , 6 , 42 , 1806...

Capuchin
Apr 29, 2009, 12:53 AM
2 possible answers are 3263442 and 3270666

Unknown008
Apr 29, 2009, 10:00 AM
I found that the next numbers have been multiplied by prime numbers... first;y by 2, then 3, then 7, then 43

And the answer of Cap, by 1807 and the other possibility, 1811 (which by the way is the next prime number)

3 is the 2rd prime number;
7 is the 3rd prime number including the 3rd prime;
But 43 isn't the 7th prime number after 7 inclusive... but the 11th..

That is quite confusing. Am I on the right track?

Perito
Apr 29, 2009, 10:11 AM
I found Capuchin's first value using this logic.

value_{n+1}=value_n\, \times\, value_n\, +\, value_n

The second value is 1 \times 1+1 = 2

6 = 2 \times2+2

42 = 6 \times 6+6

1806 = 42 \times 42+42

3263442 = 1806 \times 1806+1806

I'm not sure of Capuchin's other possibility.

Capuchin
Apr 30, 2009, 03:15 AM
Jerry, you're close to my logic, which was a(n) = a(n-1)*(next prime higher than a(n-1))

And Perito hit the logic behind my first answer, a(n) = a(n-1)^2+a(n-1)

Unknown008
Apr 30, 2009, 07:08 AM
Aha! Thanks Cap :)