This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A282506 Numbers k such that (5*10^k - 101)/3 is prime. 0
 4, 19, 29, 42, 48, 57, 70, 71, 72, 124, 189, 216, 1860, 4170, 6132, 9226, 9725, 9906, 9942, 15283, 19386, 181950 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k>1, numbers such that the digit 1 followed by k-2 occurrences of the digit 6 followed by the digits 33 is prime (see Example section). a(23) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 16w33. EXAMPLE 4 is in this sequence because (5*10^4 - 101)/3 = 16633 is prime. Initial terms and primes associated: a(1) = 4, 16633; a(2) = 19, 16666666666666666633; a(3) = 29, 166666666666666666666666666633; a(4) = 42, 1666666666666666666666666666666666666666633; a(5) = 48, 1666666666666666666666666666666666666666666666633; etc. MATHEMATICA Select[Range[2, 100000], PrimeQ[(5*10^# - 101)/3] &] PROG (PARI) isok(k) = ispseudoprime((5*10^k-101)/3); \\ Altug Alkan, Apr 19 2018 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A022135 A192193 A028564 * A003338 A047715 A031291 Adjacent sequences:  A282503 A282504 A282505 * A282507 A282508 A282509 KEYWORD nonn,more,hard AUTHOR Robert Price, Feb 16 2017 EXTENSIONS a(22) from Robert Price, Apr 19 2018 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 21 05:14 EST 2018. Contains 317428 sequences. (Running on oeis4.)