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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A281734 Numbers k such that (2*10^k + 529)/9 is prime. 1
0, 1, 3, 4, 7, 9, 16, 18, 21, 33, 34, 45, 49, 57, 567, 595, 685, 867, 1867, 4204, 5311, 11493, 13923, 19116, 30471, 32038, 34551, 99408, 113631, 134364, 195399 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that k-2 occurrences of the digit 2 followed by the digits 81 is prime (see Example section).

a(32) > 2*10^5.

LINKS

Table of n, a(n) for n=1..31.

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

Makoto Kamada, Search for 2w81.

EXAMPLE

3 is in this sequence because (2*10^3 + 529)/9 = 281 is prime.

Initial terms and primes associated:

a(1) = 0, 59;

a(2) = 1, 61;

a(3) = 3, 281;

a(4) = 4, 2281;

a(5) = 7, 2222281; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(2*10^# + 529)/9] &]

CROSSREFS

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

Sequence in context: A086772 A301767 A169898 * A086336 A237258 A108796

Adjacent sequences:  A281731 A281732 A281733 * A281735 A281736 A281737

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jan 28 2017

EXTENSIONS

a(29)-a(31) from Robert Price, Jan 02 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 31 07:22 EDT 2020. Contains 334747 sequences. (Running on oeis4.)