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 A295972 Numbers k such that (49*10^k - 139)/9 is prime. 0
 5, 6, 18, 27, 48, 51, 92, 396, 678, 1259, 2085, 2820, 3009, 4311, 5015, 7775, 7955, 8595, 120380, 166721 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers such that the digit 5 followed by k-2 occurrences of the digit 4 followed by the digits 29 is prime (see Example section). a(21) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 54w29 EXAMPLE 5 is in this sequence because (49*10^5 - 139)/9 = 544429 is prime. Initial terms and primes associated: a(1) = 5, 544429; a(2) = 6, 5444429; a(3) = 18, 5444444444444444429; a(4) = 27, 5444444444444444444444444429; etc. MATHEMATICA Select[Range[1, 100000], PrimeQ[(49*10^# - 139)/9] &] PROG (PARI) isok(k) = isprime((49*10^k - 139)/9); \\ Michel Marcus, Dec 01 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A180134 A192727 A056519 * A063445 A257331 A240400 Adjacent sequences:  A295969 A295970 A295971 * A295973 A295974 A295975 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 30 2017 EXTENSIONS a(19)-a(20) from Robert Price, Mar 04 2019 STATUS approved

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Last modified March 26 12:43 EDT 2019. Contains 321497 sequences. (Running on oeis4.)