login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

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 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A280016 Numbers k such that 8*10^k-99 is prime. 0
2, 3, 4, 9, 22, 50, 67, 82, 87, 89, 130, 134, 170, 179, 220, 832, 1425, 1648, 2356, 2434, 6556, 11391, 12610, 20278, 46509, 50253 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 01 is prime (see Example section).

a(27) > 2*10^5.

LINKS

Table of n, a(n) for n=1..26.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 79w01.

EXAMPLE

3 is in this sequence because 8*10^3-99 = 7901 is prime.

Initial terms and primes associated:

a(1) = 2, 701;

a(2) = 3, 7901;

a(3) = 4, 79901;

a(4) = 9, 7999999901;

a(5) = 22, 79999999999999999999901; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[8*10^#-99] &]

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A258274 A228126 A192988 * A122534 A101135 A280054

Adjacent sequences:  A280013 A280014 A280015 * A280017 A280018 A280019

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Feb 21 2017

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 1 01:37 EST 2021. Contains 349426 sequences. (Running on oeis4.)