A034821 Concatenations C1 and C2 are both prime (see the comment lines).

5, 17, 103, 127, 157, 191, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 227, 234, 235, 236, 237, 238, 258, 259, 260, 261, 262, 307, 347, 354, 355, 356, 357, 358, 431, 524, 525, 526, 527, 528, 529, 530, 531, 532, 533, 534, 535, 536, 537, 538, 539

Offset: 0

Author

Patrick De Geest, Oct 15 1998

Keywords

• nonn
• base

Comments

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

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

Examples

			n=17 -> next prime is 19, previous prime is 13, thus '1319' and '1913' are both primes.
		

Crossrefs

Cf. A034808-A034820.

Programs

Mathematica

c1c2pQ[n_]:=Module[{c1=NextPrime[n,-1],c2=NextPrime[n]},AllTrue[ {c1* 10^IntegerLength[ c2]+c2,c2*10^IntegerLength[c1]+c1},PrimeQ]]; Select[ Range[600],c1c2pQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 23 2019 *)