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 A278418 Numbers k such that (83*10^k - 29) / 9 is prime. 0
 1, 2, 4, 10, 28, 31, 32, 38, 68, 134, 158, 254, 311, 337, 392, 874, 2747, 3502, 4735, 6142, 14140, 17095, 20066, 21104, 26743 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers such that the digit 9 followed by k-2 occurrences of the digit 2 followed by the digits 19 is prime (see Example section). a(26) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 92w19. EXAMPLE 4 is in this sequence because (83*10^4 - 29) / 9 = 92219 is prime. Initial terms and primes associated: a(1) = 1, 89; a(2) = 2, 919; a(3) = 4, 92219; a(4) = 10, 92222222219; a(5) = 28, 92222222222222222222222222219; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(83*10^# - 29) / 9] &] PROG (PARI) isok(n) = isprime((83*10^n - 29)/9); \\ Michel Marcus, Nov 21 2016 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A005975 A048193 A123411 * A321946 A244485 A128933 Adjacent sequences:  A278415 A278416 A278417 * A278419 A278420 A278421 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 21 2016 STATUS approved

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Last modified May 16 20:03 EDT 2022. Contains 353720 sequences. (Running on oeis4.)