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 A271269 Numbers k such that 8*10^k - 49 is prime. 490
 1, 2, 3, 8, 24, 49, 57, 74, 104, 131, 144, 162, 182, 246, 302, 352, 557, 581, 589, 704, 939, 1181, 1937, 2157, 4463, 6013, 7266, 8504, 8691, 16129, 20108, 40677, 74234, 112018 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section). a(35) > 2*10^5. LINKS Makoto Kamada, Search for 79w51. EXAMPLE 3 is in this sequence because 8*10^3 - 49 = 7951 is prime. Initial terms and primes associated: a(1) = 1, 31; a(2) = 2, 751; a(3) = 3, 7951; a(4) = 8, 799999951; a(6) = 24, 7999999999999999999999951, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[8*10^# - 49] &] PROG (PARI) is(n)=isprime(8*10^n - 49) \\ Charles R Greathouse IV, Feb 16 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929. Sequence in context: A120763 A120708 A327009 * A089847 A304121 A038561 Adjacent sequences:  A271266 A271267 A271268 * A271270 A271271 A271272 KEYWORD nonn,more AUTHOR Robert Price, Apr 03 2016 EXTENSIONS a(34) from Robert Price, Aug 20 2019 STATUS approved

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Last modified January 24 07:11 EST 2020. Contains 331189 sequences. (Running on oeis4.)