A034814 Concatenations C1 and C2 are both prime (see the comment lines).

9, 51, 63, 87, 111, 123, 153, 177, 207, 211, 239, 263, 273, 289, 327, 333, 343, 359, 407, 471, 489, 497, 513, 541, 597, 621, 651, 659, 663, 681, 687, 693, 697, 747, 753, 793, 819, 831, 869, 909, 977, 987, 1027, 1041, 1089, 1131, 1143, 1239, 1491, 1611

Offset: 1

Author

Patrick De Geest, Oct 15 1998

Keywords

• nonn
• base

Comments

C1 = 'prevprime(k) followed by k'.

C2 = 'k followed by prevprime(k)'.

Examples

			n=747 -> previous prime is 743, thus '743747' and '747743' are both primes.
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A034808 and A034809.

Cf. A034810-A034821.

Extensions

Offset changed by Andrew Howroyd, Aug 13 2024