# Another number series

brobluto
Posers and Puzzles 21 Apr '08 19:34
1. 21 Apr '08 19:34
1
3
13
61

What comes next and why?
2. wolfgang59
21 Apr '08 19:40
Originally posted by brobluto
1
3
13
61

What comes next and why?
65

All are Vegetarian dishes
3. forkedknight
Defend the Universe
21 Apr '08 20:35
I'm gonna go with 26
4. 21 Apr '08 20:40
Originally posted by forkedknight
I'm gonna go with 26
Why?
5. forkedknight
Defend the Universe
22 Apr '08 01:44
Originally posted by brobluto
Why?
I was trying to think of an expression for it.

using integer division, aka dropping the remainder:
s(n+1) = 10*( s(n-1)/10 + s(n) % 10 ) + s(n)/10

where % is for modulo division
6. 22 Apr '08 02:12
My guess would be a prime number around 250-260, but I have yet to find any rule which explains how you arrive at each number.

Can we have a hint?
7. 22 Apr '08 11:50
Originally posted by geepamoogle
My guess would be a prime number around 250-260, but I have yet to find any rule which explains how you arrive at each number.

Can we have a hint?
You're on the right track with prime numbers.
8. wolfgang59
22 Apr '08 12:09
Originally posted by geepamoogle
My guess would be a prime number around 250-260, but I have yet to find any rule which explains how you arrive at each number.

Can we have a hint?
Coincidence or help? (Obviously 3 does not fit pattern)

1 = (2^2) - 3

13 = (2^4) - 3

61 = (2^6) - 3

Will that help finding your prime?

Is (2^8) - 3 = 253 in series? ðŸ™„
9. 22 Apr '08 12:16
Originally posted by wolfgang59
Coincidence or help? (Obviously 3 does not fit pattern)

1 = (2^2) - 3

13 = (2^4) - 3

61 = (2^6) - 3

Will that help finding your prime?

Is (2^8) - 3 = 253 in series? ðŸ™„
No, 253 is not in the series.
10. 22 Apr '08 12:181 edit
I apologize, the series is

1
3
13
71

One being the first prime number (I know that's somewhat debatable, but for this exercise it is)
11. 22 Apr '08 12:36
Originally posted by brobluto
One being the first prime number (I know that's somewhat debatable, but for this exercise it is)
12. 22 Apr '08 13:50
Originally posted by brobluto
You're on the right track with prime numbers.
Is 1 a prime number?
13. 22 Apr '08 14:07
Originally posted by Thomaster
Is 1 a prime number?
Not technically, no. But 1 is part of the series and hint. It's as if you started counting 1 through 10, but skipped 2, and 4-12. (although that's not the answer)
14. forkedknight
Defend the Universe
22 Apr '08 14:40
479, the 72nd prime number after 71
15. 22 Apr '08 14:46
1 is a sort of an oddball.

A prime number has exactly two integer divisors, 1 and itself.
A composite number has 3 or more divisors.

1 only has a singular divisor, itself. It is the only counting number with this property.

For most mathematical purposes, 1 isn't considered 'prime', but rather a multiplicative identity. For instance, 1 isn't listed for prime factorization of a number.

That being said, it would seem for the purposes of this pattern, 1 is considered prime, and as such I will accept it.