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 A294230 Numbers k such that (55*10^k + 377)/9 is prime. 0
 1, 2, 4, 20, 40, 61, 62, 82, 169, 172, 214, 874, 1520, 1652, 2185, 3221, 4012, 4669, 13165, 18922, 91142 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 1 followed by the digits 53 is prime (see Example section). a(22) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 61w53 EXAMPLE 2 is in this sequence because (55*10^2 + 377)/9 = 653 is prime. Initial terms and primes associated: a(1) = 1, 103; a(2) = 2, 653; a(3) = 4, 61153; a(4) = 20, 611111111111111111153; a(5) = 40, 61111111111111111111111111111111111111153; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(55*10^# + 377)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A108866 A259122 A059206 * A052004 A027741 A137697 Adjacent sequences:  A294227 A294228 A294229 * A294231 A294232 A294233 KEYWORD nonn,more,hard,changed AUTHOR Robert Price, Oct 25 2017 STATUS approved

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Last modified January 23 18:05 EST 2019. Contains 319400 sequences. (Running on oeis4.)