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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A052089 Primes formed by concatenating n with n-1. 27
43, 109, 2221, 2423, 3433, 4241, 5857, 7069, 7877, 8887, 10099, 102101, 108107, 112111, 114113, 124123, 148147, 154153, 160159, 172171, 180179, 192191, 198197, 202201, 208207, 210209, 214213, 238237, 244243, 262261, 264263, 268267, 270269 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paul Tek, Table of n, a(n) for n = 1..10000

EXAMPLE

2423 is a prime and a concatenation of 24 and 23.

MATHEMATICA

Sort[Select[FromDigits[Flatten[IntegerDigits/@#]]&/@Partition[ Range[ 300, 1, -1], 2, 1], PrimeQ]] (* Harvey P. Dale, May 09 2012 *)

PROG

(PARI) for(n=4, 1e4, if(isprime(t=eval(Str(n, n-1))), print1(t", "))) \\ Charles R Greathouse IV, May 07 2013

(MAGMA) [Seqint(Intseq(n-1) cat Intseq(n)): n in [2..300 by 2] | IsPrime(Seqint(Intseq(n-1) cat Intseq(n)))]; // Marius A. Burtea, Mar 21 2019

CROSSREFS

Cf. A030458, A052087, A052088.

Sequence in context: A142055 A052088 A068699 * A260809 A039471 A104783

Adjacent sequences:  A052086 A052087 A052088 * A052090 A052091 A052092

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Jan 15 2000

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 December 1 12:50 EST 2020. Contains 338833 sequences. (Running on oeis4.)