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 A273097 Numbers k such that 4*10^k + 87 is prime. 0
 1, 2, 4, 5, 13, 25, 27, 32, 37, 38, 40, 45, 57, 80, 91, 151, 214, 441, 644, 764, 797, 2329, 2931, 4324, 21794, 22396, 24041, 1222, 46420, 51489, 55165, 126625 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section). a(33) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 40w87. EXAMPLE 4 is in this sequence because 4*10^4 + 87 = 40087 is prime. Initial terms and primes associated: a(1) = 1, 127: a(2) = 2, 487; a(3) = 4, 40087; a(4) = 5, 400087; a(5) = 13, 40000000000087, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[4*10^# + 87] &] PROG (PARI) is(n)=ispseudoprime(4*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A078652 A289491 A102992 * A232207 A136563 A127077 Adjacent sequences:  A273094 A273095 A273096 * A273098 A273099 A273100 KEYWORD nonn,more AUTHOR Robert Price, May 15 2016 EXTENSIONS a(32) from Robert Price, Aug 15 2018 STATUS approved

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Last modified April 9 18:31 EDT 2020. Contains 333361 sequences. (Running on oeis4.)