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A175734
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Largest n-digit number with 3 divisors.
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7
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9, 49, 961, 9409, 97969, 994009, 9840769, 99460729, 999002449, 9998200081, 99996985729, 999966000289, 9999995824729, 99999820000081, 999997874844049, 9999997800000121, 99999977853408361, 999999874000003969, 9999999828172082689, 99999999340000001089
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OFFSET
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1,1
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COMMENTS
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Because every number with exactly three divisors must be the square of a prime, the last digit of each term in this sequence is either 1 or 9. [From Harvey P. Dale, Aug 18 2011, with thanks to Ant King and Chris Gribble]
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LINKS
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Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
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FORMULA
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a(n) = A132153(n)^2.
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MATHEMATICA
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Join[{9}, Table[NextPrime[Sqrt[10^n-1], -1]^2, {n, 2, 20}]](* Harvey P. Dale, Aug 18 2011 *)
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PROG
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(MAGMA) A175734 := func<n|PreviousPrime(Isqrt(10^n)+1)^2>; /* From Jason Kimberley, Aug 18 2011 */
(PARI) A175734(n)=precprime(sqrtint(10^n))^2 \\ M. F. Hasler, Aug 18 2011
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CROSSREFS
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Cf. A131581, A132153, A136582, A175733.
Sequence in context: A160603 A115326 A069666 * A174744 A133049 A188140
Adjacent sequences: A175731 A175732 A175733 * A175735 A175736 A175737
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KEYWORD
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nonn,base
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AUTHOR
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Jaroslav Krizek, Aug 24 2010
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EXTENSIONS
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a(14)-a(20) from Harvey P. Dale, Aug 18 2011
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STATUS
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approved
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