A134428 Primes formed by concatenating k with k+1, where k+1 is a prime.

23, 67, 1213, 3637, 4243, 7879, 9697, 102103, 108109, 126127, 138139, 150151, 156157, 180181, 192193, 270271, 276277, 312313, 330331, 378379, 420421, 432433, 438439, 456457, 522523, 540541, 546547, 576577, 600601, 606607, 612613, 618619

Offset: 1

Author

Paolo P. Lava and Giorgio Balzarotti, Jan 18 2008

Keywords

• nonn
• base
• easy

Comments

Subset of A030458 and A052087.

Links

• Paolo P. Lava, Table of n, a(n) for n = 1..2500

Crossrefs

Cf. A030458, A052087.

Programs

Maple

P:=proc(n) local a;
a:=(ithprime(n)-1)*10^(ilog10(ithprime(n))+1)+ithprime(n);
if isprime(a) then a; fi; end: seq(P(i),i=1..10^3);

Mathematica

Select[Table[(p-1)*10^IntegerLength[p]+p,{p,Prime[Range[200]]}],PrimeQ] (* Harvey P. Dale, Aug 23 2019 *)