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A089329
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Smallest k such that the concatenation r*k for r = 1 to n followed by a 1 is a prime.
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1
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1, 2, 1, 7, 2, 2, 24, 8, 1, 103, 1, 12, 43, 94, 21, 1, 11, 12, 4, 23, 27, 4, 89, 20, 42, 1, 43, 6, 41, 44, 190, 22, 12, 139, 41, 114, 16, 3, 26, 171, 32, 220, 78, 86, 135, 117, 21, 44, 49, 143, 248, 175, 9, 76, 6, 66, 426, 46, 237, 252, 9, 62, 319, 88, 150, 123, 61, 122, 300, 15
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| a(4) = 7 and the prime is 71421281= A089328(4).
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MATHEMATICA
| Do[s = ""; k = 0; While[ !PrimeQ[ToExpression[s]], s = ""; k++; For[r = 1, r <= n, r++, s = s <> ToString[r*k]]; s = s <> "1"]; Print[k], {n, 1, 50}] (Propper)
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CROSSREFS
| Cf. A089328.
Sequence in context: A124392 A144446 A121416 * A200236 A097411 A134929
Adjacent sequences: A089326 A089327 A089328 * A089330 A089331 A089332
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 04 2003
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EXTENSIONS
| Corrected and extended by Ryan Propper (rpropper(AT)stanford.edu), Jul 24 2005
More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Sep 13 2005
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