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ehrenfest
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[SOLVED] larson 4.1.8
Let N be the number which when expressed in decimal notation consists of 91 ones:
1111...1111 = N
Prove that N is a composite number.
If N had an even number n of ones we could use the fact that
[tex]\sum_{i=0}^n x^i = (1+x)(x+x^3+x^5+...+x^{n-1}) = N [/tex]
evaluated at x=10. I tried doing lots of similar tricks for the odd case but nothing seems to factor completely.
Homework Statement
Let N be the number which when expressed in decimal notation consists of 91 ones:
1111...1111 = N
Prove that N is a composite number.
Homework Equations
The Attempt at a Solution
If N had an even number n of ones we could use the fact that
[tex]\sum_{i=0}^n x^i = (1+x)(x+x^3+x^5+...+x^{n-1}) = N [/tex]
evaluated at x=10. I tried doing lots of similar tricks for the odd case but nothing seems to factor completely.