1. Joined
    04 Oct '06
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    11845
    21 Apr '08 19:34
    1
    3
    13
    61

    What comes next and why?
  2. Standard memberwolfgang59
    howling mad
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    21 Apr '08 19:40
    Originally posted by brobluto
    1
    3
    13
    61

    What comes next and why?
    65









    All are Vegetarian dishes
  3. Standard memberforkedknight
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    21 Apr '08 20:35
    I'm gonna go with 26
  4. Joined
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    21 Apr '08 20:40
    Originally posted by forkedknight
    I'm gonna go with 26
    Why?
  5. Standard memberforkedknight
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    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. Joined
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    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. Joined
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    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. Standard memberwolfgang59
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    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? 🙄
  9. Joined
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    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? 🙄
    No, 253 is not in the series.
  10. Joined
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    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. Joined
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    35068
    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)
    For "debatable" read "wrong" 🙂
  12. ALG
    Joined
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    22 Apr '08 13:50
    Originally posted by brobluto
    You're on the right track with prime numbers.
    Is 1 a prime number?
  13. Joined
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    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. Standard memberforkedknight
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    22 Apr '08 14:40
    479, the 72nd prime number after 71
  15. Joined
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    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.
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