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!)
A294944 Numbers k such that (76*10^k + 113)/9 is prime. 0
1, 2, 4, 5, 8, 13, 14, 26, 44, 58, 61, 83, 256, 878, 1513, 3122, 6398, 6476, 8683, 18482, 33917, 45937, 64534 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 8 followed by k-2 occurrences of the digit 4 followed by the digits 57 is prime (see Example section).

a(24) > 2*10^5.

LINKS

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 84w57.

EXAMPLE

2 is in this sequence because (76*10^2 + 113)/9 = 857 is prime.

Initial terms and primes associated:

a(1) = 1, 97;

a(2) = 2, 857;

a(3) = 4, 84457;

a(4) = 5, 844457;

a(5) = 8, 844444457; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(76*10^# + 113)/9] &] (* Corrected by Georg Fischer, Jul 22 2019 *)

PROG

(PARI) isok(k) = isprime((76*10^k + 113)/9); \\ Michel Marcus, Nov 12 2017

CROSSREFS

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

Sequence in context: A031988 A023745 A217136 * A178656 A085443 A164571

Adjacent sequences:  A294941 A294942 A294943 * A294945 A294946 A294947

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 11 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 July 8 17:40 EDT 2020. Contains 335524 sequences. (Running on oeis4.)