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 A291607 Numbers k such that (46*10^k + 521)/9 is prime. 0
 1, 2, 4, 5, 8, 29, 43, 62, 85, 107, 172, 557, 1043, 2395, 4498, 5818, 7772, 9125, 12616, 17252, 23000, 64904, 71077, 113162 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 1 followed by the digits 69 is prime (see Example section). a(25) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 51w69 EXAMPLE 4 is in this sequence because (46*10^4 + 521)/9 = 51169 is prime. Initial terms and primes associated: a(1) = 1, 109; a(2) = 2, 569; a(3) = 4, 51169; a(4) = 5, 511169; a(5) = 8, 511111169; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(46*10^# + 521)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A277289 A218347 A171411 * A092752 A152603 A159260 Adjacent sequences:  A291604 A291605 A291606 * A291608 A291609 A291610 KEYWORD nonn,more,hard AUTHOR Robert Price, Aug 27 2017 EXTENSIONS a(24) from Robert Price, Feb 23 2019 STATUS approved

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Last modified May 31 02:51 EDT 2020. Contains 334747 sequences. (Running on oeis4.)