A034595 Concatenation of 'nextprime(a(n)) and a(n)' and 'a(n) and nextprime(a(n))' are both prime.

27, 51, 63, 123, 199, 217, 219, 233, 257, 341, 353, 357, 417, 423, 429, 473, 501, 519, 523, 551, 579, 597, 609, 653, 657, 667, 669, 687, 703, 717, 777, 783, 801, 873, 891, 971, 987, 1017, 1043, 1139, 1157, 1161, 1271, 1337, 1343, 1389, 1671, 1973, 2019

Offset: 1

Author

Patrick De Geest, Oct 15 1998

Keywords

• nonn
• base

Examples

			a(n)=353 -> nextprime(a(n)) is 359 so '353359' and '359353' are both prime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A034591 and A034594.

Cf. A034596, A034808, A034809, A034814.

Programs

Mathematica

bpQ[n_]:=Module[{np=NextPrime[n]},AllTrue[{n*10^IntegerLength[np]+ np, np* 10^IntegerLength[ n]+n}, PrimeQ]]; Select[Range[2100],bpQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 19 2016 *)

Extensions

Offset changed by Andrew Howroyd, Aug 13 2024