A034815 Concatenations C1 and C2 are both prime (see the comment lines).

33, 51, 53, 63, 111, 123, 129, 211, 237, 273, 357, 489, 519, 573, 597, 609, 639, 651, 653, 657, 669, 681, 687, 747, 753, 819, 831, 873, 891, 987, 997, 1071, 1611, 1881, 2037, 2049, 2247, 2271, 2613, 2763, 3063, 3267, 3393, 3573, 3969, 4251, 4263, 4293

Offset: 0

Author

Patrick De Geest, Oct 15 1998

Keywords

• nonn
• base

Comments

C1 = 'nextprime(n) followed by n'

C2 = 'n followed by prevprime(n)'

Examples

			n=1881 -> next prime is 1889, previous prime is 1879, thus '18891881' and '18811879' are both primes.
		

Crossrefs

Cf. A034808-A034821.

Programs

Mathematica

okQ[n_]:=Module[{idn=IntegerDigits[n],ida,idb},ida=IntegerDigits[NextPrime[n,-1]];idb=IntegerDigits[NextPrime[n]];PrimeQ[FromDigits[Join[idn,ida]]]&&PrimeQ[FromDigits[Join[idb,idn]]]]
Select[Range[5000],okQ]  (* Harvey P. Dale, Dec 25 2010 *)