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

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60, we have over 367,000 sequences, and we’ve crossed 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A288149 Numbers k such that (68*10^k - 257)/9 is prime. 0
 1, 2, 4, 8, 11, 20, 22, 32, 40, 62, 95, 104, 569, 710, 955, 1682, 2933, 4592, 10286, 16634, 19235, 20437, 31024, 48304, 79813, 128645, 148060 (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 5 followed by the digits 27 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 75w27. EXAMPLE 4 is in this sequence because (68*10^4 - 257)/9 = 75527 is prime. Initial terms and primes associated: a(1) = 1, 47; a(2) = 2, 727; a(3) = 4, 75527; a(4) = 8, 755555527; a(5) = 11, 755555555527; etc. MATHEMATICA Select[Range[1, 100000], PrimeQ[(68*10^# - 257)/9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A033956 A282620 A320440 * A159693 A363735 A053437 Adjacent sequences: A288146 A288147 A288148 * A288150 A288151 A288152 KEYWORD nonn,more,hard AUTHOR Robert Price, Jun 05 2017 EXTENSIONS a(26)-a(27) from Robert Price, Jul 27 2019 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 December 1 23:26 EST 2023. Contains 367503 sequences. (Running on oeis4.)