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!)
A249380 Prime numbers Q such that the concatenation Q,8,Q is prime. 3
3, 7, 19, 61, 67, 109, 139, 277, 337, 349, 523, 547, 727, 751, 823, 853, 859, 883, 991, 1009, 1063, 1093, 1231, 1237, 1279, 1291, 1321, 1423, 1429, 1447, 1531, 1609, 1657, 1723, 1759, 1867, 1933, 1951, 2089, 2113, 2131, 2683 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..10000

EXAMPLE

383 is prime so a(1)=3.

585 is composite, 787 is prime so a(2)=7.

PROG

(PFGW & SCRIPT), the pre10.txt file with the first 10000000 prime numbers.

SCRIPT

DIM i, 0

DIM j

DIM k

DIM n, 1

OPENFILEOUT myf, a(n).txt

OPENFILEIN maf, pre10.txt

GETNEXT j, maf

LABEL loop1

GETNEXT j, maf

IF j>10^n THEN SET n, n+1

SET k, j*10^(n+1)+8*10^n+j

PRP k

IF ISPRP THEN GOTO w

GOTO loop1

LABEL w

SET i, i+1

WRITE myf, j

IF i>9999 THEN END

GOTO loop1

(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 8), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014

(MAGMA) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [8] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014

CROSSREFS

Cf. similar sequences listed in A249374.

Sequence in context: A148667 A148668 A148669 * A210985 A160128 A051139

Adjacent sequences:  A249377 A249378 A249379 * A249381 A249382 A249383

KEYWORD

nonn,base

AUTHOR

Pierre CAMI, Oct 27 2014

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 April 8 08:04 EDT 2020. Contains 333313 sequences. (Running on oeis4.)