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!)
A165243 Primes obtained from other primes by pre-concatenating with 2. 7
23, 211, 223, 229, 241, 271, 283, 2113, 2131, 2137, 2179, 2239, 2251, 2269, 2281, 2293, 2311, 2347, 2383, 2389, 2467, 2503, 2521, 2557, 2593, 2617, 2647, 2659, 2677, 2683, 2719, 2797, 2857, 2887, 2953, 2971, 21013, 21019, 21031, 21061, 21163, 21187 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..42.

EXAMPLE

The prime 2971 is from the prime 971 by pre-concatenating with 2.

MATHEMATICA

Select[Map[FromDigits,

Map[Join[{2}, #] &, IntegerDigits[Prime[Range[200]]]]], PrimeQ[#] &] (* Robert Price, Mar 31 2019 *)

PROG

(PARI) terms(n) = my(i=0, cc=[]); forprime(p=1, , cc=eval(concat("2", Str(p))); if(ispseudoprime(cc), print1(cc, ", "); i++); if(i==n, break))

/* Print initial 40 terms as follows: */

terms(40) \\ Felix Fröhlich, Mar 31 2019

CROSSREFS

Cf. A000040

Sequence in context: A322287 A327918 A327919 * A142374 A171342 A112747

Adjacent sequences:  A165240 A165241 A165242 * A165244 A165245 A165246

KEYWORD

base,nonn

AUTHOR

Parthasarathy Nambi, Sep 09 2009

EXTENSIONS

2269 inserted by R. J. Mathar, Sep 21 2009

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 6 20:06 EDT 2020. Contains 333286 sequences. (Running on oeis4.)