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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A100003 Prime numbers n such that the concatenation of all odd primes up through n in decreasing order is prime. 6
3, 5, 17, 89, 383, 8831 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Next term is greater than 4400th prime and the prime corresponding to the next term has more than 20000 digits. Number of digits of primes corresponding to the six known terms of the sequence are respectively 1, 2, 9, 43, 198, 4202.

We can see the prime corresponding to 383 (the 5th term of the sequence) in the page related to puzzle 8 of the website of Carlos Rivera.

a(7) > prime(28800) = 335033. - Giovanni Resta, Apr 01 2013

LINKS

Table of n, a(n) for n=1..6.

C. Rivera, Primes by Listing.

EXAMPLE

17 is in the sequence because 17.13.11.7.5.3 is prime (dot between numbers means concatenation).

MATHEMATICA

Do[If[PrimeQ[(v={}; Do[v=Join[v, IntegerDigits[Prime[n-j+1]]], {j, n-1}]; FromDigits[v])], Print[Prime[n]]], {n, 2, 4413}]

Prime[#]&/@Select[Range[100], PrimeQ[FromDigits[Flatten[IntegerDigits/@ Prime[Range[#, 2, -1]]]]]&] (* To generate a(6) increase the Range by 1000, but the program will run a long time. *) (* Harvey P. Dale, Nov 27 2015 *)

CROSSREFS

Cf. A046284, A099070, A099071, A099073.

The actual prime concatenations in A092448 and the original concatenations in A092447. - Dmitry Kamenetsky, Mar 02 2009

Sequence in context: A227335 A281627 A102846 * A283331 A114161 A174722

Adjacent sequences:  A100000 A100001 A100002 * A100004 A100005 A100006

KEYWORD

base,more,nonn,nice

AUTHOR

Farideh Firoozbakht, Nov 06 2004

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified August 24 02:32 EDT 2017. Contains 291052 sequences.