A165243 Primes obtained from other primes by pre-concatenating with 2.

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

Offset: 1

Author

Parthasarathy Nambi, Sep 09 2009

Keywords

• base
• nonn

Examples

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

Crossrefs

Cf. A000040

Programs

Mathematica

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

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

Extensions

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