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

0,1

Comments

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

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

Links

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

Example

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

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 *)

Crossrefs

Cf. A034808-A034821.

Sequence in context: A024975 A025399 A171390 * A319602 A262796 A255101

Adjacent sequences: A034810 A034811 A034812 * A034814 A034815 A034816

Keyword

nonn,base

Author

Patrick De Geest, Oct 15 1998

Status

approved