login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A295398 Numbers k such that (305*10^k + 1)/9 is prime. 0
2, 3, 12, 14, 38, 126, 147, 152, 216, 285, 774, 1458, 2049, 3369, 5718, 8358, 12510, 13863, 30308, 38732 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that the digits 33 followed by k-1 occurrences of the digit 8 followed by the digit 9 is prime (see Example section).

a(21) > 10^5.

LINKS

Table of n, a(n) for n=1..20.

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

Makoto Kamada, Search for 338w9

EXAMPLE

2 is in this sequence because (305*10^2 + 1)/9 = 3389 is prime.

Initial terms and primes associated:

a(1) = 2, 3389;

a(2) = 3, 33889;

a(3) = 12, 33888888888889;

a(4) = 14, 3388888888888889;

a(5) = 38, 3388888888888888888888888888888888888889; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(305*10^# + 1)/9] &]

PROG

(PARI) isok(k) = isprime((305*10^k + 1)/9); \\ Michel Marcus, Nov 22 2017

CROSSREFS

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

Sequence in context: A299545 A068603 A045878 * A138321 A015756 A163906

Adjacent sequences:  A295395 A295396 A295397 * A295399 A295400 A295401

KEYWORD

nonn,more,hard,changed

AUTHOR

Robert Price, Nov 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 January 22 18:06 EST 2019. Contains 319365 sequences. (Running on oeis4.)