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 A295398 Numbers k such that (305*10^k + 1)/9 is prime. 0
 2, 3, 12, 14, 38, 126, 147, 152, 216, 285, 774, 1458, 2049, 3369, 5718, 8358, 12510, 13863, 30308, 38732, 128198 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers such that the digits 33 followed by k-1 occurrences of the digit 8 followed by the digit 9 is prime (see Example section). a(22) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 338w9. EXAMPLE 2 is in this sequence because (305*10^2 + 1)/9 = 3389 is prime. Initial terms and primes associated: a(1) = 2, 3389; a(2) = 3, 33889; a(3) = 12, 33888888888889; a(4) = 14, 3388888888888889; a(5) = 38, 3388888888888888888888888888888888888889; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(305*10^# + 1)/9] &] PROG (PARI) isok(k) = isprime((305*10^k + 1)/9); \\ Michel Marcus, Nov 22 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A299545 A068603 A045878 * A138321 A015756 A163906 Adjacent sequences:  A295395 A295396 A295397 * A295399 A295400 A295401 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 21 2017 EXTENSIONS a(21) from Robert Price, Jan 31 2020 STATUS approved

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Last modified May 26 13:49 EDT 2020. Contains 334626 sequences. (Running on oeis4.)