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 A272193 Numbers k such that (73*10^k + 143)/9 is prime. 0
 1, 2, 5, 7, 13, 16, 17, 25, 44, 52, 197, 233, 241, 389, 838, 856, 2252, 2945, 5207, 8020, 10708, 14663, 16885, 20366, 20450, 24121, 24437, 29348, 134939 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers n such that the digit 8 followed by k-2 occurrences of the digit 1 followed by the digits 27 is prime (see Example section). a(29) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 81w27. EXAMPLE 5 is in this sequence because (73*10^5 + 143)/9 = 811127 is prime. Initial terms and primes associated: a(1) = 1, 97; a(2) = 2, 827;; a(3) = 5, 811127; a(4) = 7, 81111127; a(5) = 13, 81111111111127, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(73*10^# + 143)/9] &] PROG (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((73*10^n + 143)/9), print1(n, ", "))); \\ Altug Alkan, Apr 22 2016 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A121218 A266001 A062879 * A186131 A284191 A065897 Adjacent sequences: A272190 A272191 A272192 * A272194 A272195 A272196 KEYWORD nonn,more AUTHOR Robert Price, Apr 22 2016 EXTENSIONS a(29) from Robert Price, Jul 31 2019 STATUS approved

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Last modified December 4 23:46 EST 2022. Contains 358572 sequences. (Running on oeis4.)