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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A284779 Numbers k such that (13*10^k + 161)/3 is prime. 0
 1, 2, 17, 34, 52, 54, 495, 505, 572, 750, 959, 1574, 2557, 3734, 4069, 11201, 13411, 16569, 17032, 17720, 19906, 23781, 36076, 56624, 84179, 117249, 159147 (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 3 followed by the digits 87 is prime (see Example section). a(28) > 2*10^5. LINKS Table of n, a(n) for n=1..27. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 43w87. EXAMPLE 4 is in this sequence because (13*10^2 + 161)/3 = 487 is prime. Initial terms and associated primes: a(1) = 1, 97; a(2) = 2, 487; a(3) = 17, 433333333333333387; a(4) = 34, 43333333333333333333333333333333387; a(5) = 52, 43333333333333333333333333333333333333333333333333387; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(13*10^# + 161)/3] &] PROG (PARI) isok(n) = isprime((13*10^n + 161)/3); \\ Indranil Ghosh, Apr 02 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A307690 A100294 A192453 * A018529 A342485 A342487 Adjacent sequences: A284776 A284777 A284778 * A284780 A284781 A284782 KEYWORD nonn,more,hard AUTHOR Robert Price, Apr 02 2017 EXTENSIONS a(26)-a(27) from Robert Price, Nov 29 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 23 09:37 EDT 2024. Contains 374547 sequences. (Running on oeis4.)