A280576 Primes formed from the concatenation of previousprime(n) and n.

23, 79, 3137, 3739, 4751, 6163, 8387, 8389, 109111, 113117, 113123, 151153, 151157, 157163, 167173, 173177, 181183, 199207, 199211, 211213, 211217, 211219, 233239, 241249, 251257, 257263, 263267, 263269, 271273, 271277, 277279, 283289, 317321, 317323, 317327

Offset

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..7768

Example

79 is in the sequence because it is a prime formed from the concatenation of 7 and 9, where 7 is the largest prime < 9.
8387 is in the sequence because it is a prime formed from the concatenation of 83 and 87, where 83 is the largest prime < 87.

Mathematica

Select[Table[FromDigits[Join[IntegerDigits[Prime[PrimePi[n - 1]]], IntegerDigits[n]]], {n, 3, 1000}], PrimeQ]

Prog

(Magma) [p : n in[3..200] | IsPrime (p) where p is Seqint (Intseq (n) cat Intseq (PreviousPrime (n)))];
(PARI) terms(n) = my(i=0, x=3); while(1, my(cc=eval(Str(precprime(x-1), x))); if(ispseudoprime(cc), print1(cc, ", "); i++); if(i==n, break); x++)
/* Print initial 40 terms as follows: */
terms(40) \\ Felix Fröhlich, Jan 05 2017

Crossrefs

Cf. A000040, A084667, A084669, A151799, A151800, A280357, A280388.

Sequence in context: A364148 A142650 A078597 * A160297 A210706 A304592

Adjacent sequences: A280573 A280574 A280575 * A280577 A280578 A280579

Keyword

nonn,base

Author

K. D. Bajpai, Jan 05 2017

Status

approved