The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A279171 Numbers k such that (13*10^k - 73) / 3 is prime. 0
 1, 2, 5, 9, 12, 14, 36, 61, 79, 96, 121, 126, 131, 149, 175, 204, 359, 404, 533, 782, 1869, 1950, 2712, 2915, 66551 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 09 is prime (see Example section). a(26) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 43w09. EXAMPLE 5 is in this sequence because (13*10^5 - 73) / 3 = 433309 is prime. Initial terms and primes associated: a(1) = 1, 19; a(2) = 2, 409; a(3) = 5, 433309; a(4) = 9, 4333333309; a(5) = 12, 4333333333309; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(13*10^# - 73) / 3] &] PROG (PARI) is(n)=ispseudoprime((13*10^n - 73)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A191104 A287387 A287409 * A297465 A108165 A063957 Adjacent sequences:  A279168 A279169 A279170 * A279172 A279173 A279174 KEYWORD nonn,more,hard AUTHOR Robert Price, Dec 07 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 25 18:32 EST 2022. Contains 350572 sequences. (Running on oeis4.)