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 A111473 a(1) = 3, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime. 6
 3, 1, 1, 11, 113, 7, 23, 41, 37, 141, 733, 241, 3, 791, 781, 701, 239, 441, 2019, 189, 2071, 401, 851, 463, 4421, 497, 2267, 213, 1653, 1683, 1227, 667, 3261, 6673, 5799, 3579, 1907, 6483, 7813, 2443, 1923, 11439, 6657, 7861, 1847, 7521, 8277, 8459 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE 3,311,311111,31111111111111 are all prime. 31111111111111 = one copy of 3, two copies of 1, three copies of 1, four copies of 11. PROG (PARI) { x=3; for(n=2, 50, k=0; until(ispseudoprime(y), k++; y=eval(concat(Str(x), concat(vector(n, i, Str(k))))); ); print1(k, ", "); x=y; ) } \\ Max Alekseyev, May 18 2009 CROSSREFS Cf. A111471, A111472, A111474. Sequence in context: A176468 A176421 A168552 * A234944 A067402 A113340 Adjacent sequences:  A111470 A111471 A111472 * A111474 A111475 A111476 KEYWORD base,hard,nonn AUTHOR Amarnath Murthy, Aug 05 2005 EXTENSIONS More terms from Max Alekseyev, May 18 2009 STATUS approved

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Last modified June 17 22:14 EDT 2021. Contains 345086 sequences. (Running on oeis4.)