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A232769
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Numbers n not divisible by 9 such that n divides 10^n - 1 (A014950).
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2
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1, 3, 111, 4107, 151959, 5622483, 22494039, 208031871, 225121209, 832279443, 7697179227, 8329484733, 27486820443, 30794339391, 92366302683, 123199851603, 230915528769, 284795631399, 308190935121, 1017012356391
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OFFSET
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1,2
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COMMENTS
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The above terms reduced modulo 9 yield: 1, 3, 3, 3, 3, 3, 6, 3, 6, 6, 3, 6, 3, 6, 3, 3, 3, 3, 6, 3, 6, …, .
The only primes less than a billion which can divide members of this sequence are 3, 37, 5477, 607837, 1519591, 2028119, 15195911, 18235093, 44988079, 74202397, 247629013, 337349203, 395397319, 462411133, and 674699071. - Charles R Greathouse IV, Dec 03 2013
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LINKS
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MATHEMATICA
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k = 3; lst = {1}; While[k < 10^10 + 1, If[ PowerMod[10, k, k] == 1, AppendTo[ lst, k]; Print@ k]; k += 3; If[ PowerMod[ 10, k, k] == 1, AppendTo[ lst, k]; Print@ k]; k += 6]; lst
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PROG
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(PARI) forstep(n=1, 1e8, [2, 4, 4, 2, 4, 2, 2, 2, 6, 2, 2, 4, 2, 2, 2, 4, 2, 2, 2, 4, 2, 2, 6, 2, 2, 2, 4, 2, 4, 4, 2, 2], if(Mod(10, n)^n==1, print1(n", "))) \\ Charles R Greathouse IV, Dec 03 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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