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How do you find the sum of the digits of number N? Say N = 10

  1. Jan 12, 2004 #1
    How do you find the sum of the digits of number N?

    Say N = 10
  2. jcsd
  3. Jan 12, 2004 #2
    If memory serves me correctly:

    \sum_{k=1}^N k= \frac{N(N+1)}2

    a fact that you would prove by induction.
  4. Jan 13, 2004 #3


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    Was that what was meant? The "sum of the digits" of 10 is 1+ 0= 1, of course.
  5. Jan 13, 2004 #4
    It will be true only if the digits form a Arithmetic Projection
    for eg N=2468 etc {2+4+6+8}
    but not in general say for N=12245 {1+2+2+4+5}
  6. Jan 13, 2004 #5
    You're right, I answered a completely different question. Well, I am sure someone asked my question somewhere, sometime. :)
  7. Jan 13, 2004 #6

    Yea what if N = 1231247839783924723840723084732084738274... + ... N?
  8. Jan 14, 2004 #7
    Ofcourse it would be
    as N=1+0
    here it will be N=1+2+3+1+2+4+7+8+3+9+7+8+3+9+2+4+7+2+3+8+4+0+7+2+3+0+8+4+7+3+2+0+8+4+7+3+8+2+7+4+...+x+y+z+a+b+c+d :wink: :wink: :wink:
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