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 A089329 Smallest k such that the concatenation r*k for r = 1 to n followed by a 1 is a prime. 1
 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; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE a(4) = 7 and the prime is 71421281 = A089328(4). 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}] (* Ryan Propper, Jul 24 2005 *) CROSSREFS Cf. A089328. Sequence in context: A144446 A121416 A317547 * A213053 A200236 A292191 Adjacent sequences: A089326 A089327 A089328 * A089330 A089331 A089332 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 04 2003 EXTENSIONS Corrected and extended by Ryan Propper, Jul 24 2005 More terms from David Wasserman, Sep 13 2005 STATUS approved

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Last modified December 6 11:34 EST 2022. Contains 358631 sequences. (Running on oeis4.)