A034813 Concatenations C1 and C2 are both prime (see the comment lines).

36, 74, 104, 132, 188, 222, 224, 305, 317, 344, 367, 368, 389, 457, 458, 475, 540, 572, 584, 608, 631, 676, 682, 689, 697, 738, 756, 760, 781, 797, 829, 841, 893, 910, 911, 914, 928, 982, 1018, 1104, 1122, 1178, 1186, 1317, 1328, 1391, 1402, 1406, 1518

Offset: 0

Author

Patrick De Geest, Oct 15 1998

Keywords

• nonn
• base

Comments

C1 = 'prevprime(n) followed by n followed by nextprime(n)'

C2 = 'nextprime(n) followed by n followed by prevprime(n)'

Examples

			n=797 -> previous prime is 787, next prime is 809, thus '787797809' and '809797787' are both primes.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A034808-A034821.

Programs

Mathematica

c1c2Q[n_]:=Module[{ia=IntegerDigits[NextPrime[n,-1]],ib=IntegerDigits[n], ic= IntegerDigits[NextPrime[n]]}, AllTrue[{FromDigits[Join[ia,ib,ic]], FromDigits[Join[ic,ib,ia]]},PrimeQ]]; Select[Range[1600],c1c2Q] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Apr 06 2018 *)