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 A284638 Numbers k such that (4*10^k + 149)/9 is prime. 0
 0, 2, 3, 6, 12, 15, 17, 24, 26, 30, 156, 341, 519, 1284, 1455, 1841, 1874, 3410, 3890, 6185, 8472, 8696, 67784, 72174, 84779, 87669, 99693, 114296, 119474, 152253, 183659 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that k-2 occurrences of the digit 4 followed by the digits 61 is prime (see Example section). a(32) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 4w61. EXAMPLE 3 is in this sequence because (4*10^3 + 149)/9 = 461 is prime. Initial terms and primes associated: a(1) = 0, 17; a(2) = 2, 61; a(3) = 3, 461; a(4) = 6, 444461; a(5) = 12, 444444444461; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(4*10^# + 149)/9] &] PROG (PARI) isok(k) = ispseudoprime((4*10^k + 149)/9); \\ Altug Alkan, Apr 12 2018 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A291174 A281110 A252792 * A111271 A217647 A070926 Adjacent sequences: A284635 A284636 A284637 * A284639 A284640 A284641 KEYWORD nonn,more,hard AUTHOR Robert Price, Mar 30 2017 EXTENSIONS a(28)-a(31) from Robert Price, Apr 12 2018 STATUS approved

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Last modified March 21 19:39 EDT 2023. Contains 361410 sequences. (Running on oeis4.)