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Search: id:A065080
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| A065080 |
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The number of near repunit primes that can be formed from R_n (A004022), i.e. change just one digit from 1 to 0 and test for primality. |
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3
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| 0, 0, 1, 0, 1, 1, 0, 2, 1, 0, 0, 5, 0, 0, 0, 0, 2, 5, 0, 4, 0, 0, 0, 3, 0, 1, 0, 0, 1, 2, 0, 4, 1, 0, 1, 2, 0, 2, 1, 0, 0, 7, 0, 4, 0, 0, 0, 2, 0, 2, 1, 0, 1, 3, 0, 1, 0, 0, 0, 0, 0, 3, 0, 0, 0, 4, 0, 2, 0, 0, 0, 3, 0, 1, 0, 0, 1, 3, 0, 1, 0, 0, 1, 3, 0, 3, 0, 0, 1, 1, 0, 1, 0, 0, 0, 2, 0, 3, 0, 0
(list; graph; listen)
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OFFSET
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1,8
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LINKS
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Chris Caldwell, Below are all of the 12-digit Near-Repunit primes:
Chris Caldwell, Repunits
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EXAMPLE
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a(12) = 5 because from (10^12 -1)/9 = 111111111111, by changing just one digit from 1 to 0, out of the eleven candidates, 111111111101, 111111110111, 111111011111, 111011111111 and 101111111111 are primes.
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MATHEMATICA
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a = {}; Do[ p = IntegerDigits[ (10^n - 1)/9 ]; c = 0; Do[ If[ q = FromDigits[ ReplacePart[p, 0, i]]; PrimeQ[q], c++ ], {i, 2, n} ]; a = Append[a, c], {n, 1, 100} ]; a
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CROSSREFS
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Cf. A004022, A065074, A065083.
Sequence in context: A094449 A136129 A034093 this_sequence A057150 A105868 A057275
Adjacent sequences: A065077 A065078 A065079 this_sequence A065081 A065082 A065083
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 19 2001
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