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 A290476 Numbers k such that (38*10^k + 691)/9 is prime. 0
 2, 4, 8, 10, 14, 16, 29, 106, 179, 197, 365, 371, 557, 857, 862, 1163, 1454, 2206, 5075, 22384, 149999, 196792 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers such that the digit 4 followed by k - 2 occurrences of the digit 2 followed by the digits 99 is prime (see Example section). There are no multiples of 3 in the sequence, since (38 * 10^k + 691)/9 is a multiple of 3 if k is. a(23) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 42w99. EXAMPLE 4 is in this sequence because (38*10^4 + 691)/9 = 42299 is prime. Initial terms and primes associated: a(1) = 2, 499; a(2) = 4, 42299; a(3) = 8, 422222299; a(4) = 10; 42222222299; a(5) = 14, 422222222222299; etc. MATHEMATICA Select[Range[1000], PrimeQ[(38*10^# + 691)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A125499 A240092 A153974 * A189670 A034822 A300781 Adjacent sequences:  A290473 A290474 A290475 * A290477 A290478 A290479 KEYWORD nonn,more,hard AUTHOR Robert Price, Aug 03 2017 EXTENSIONS a(21)-a(22) from Robert Price, Oct 31 2018 STATUS approved

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Last modified December 9 22:37 EST 2018. Contains 318032 sequences. (Running on oeis4.)