A099084 Numbers k such that 1.2. ... .k-1.k + 4 is a prime (dot between numbers means concatenation).

1, 3, 27, 663, 6919

Offset: 1

Author

Farideh Firoozbakht, Nov 03 2004

Keywords

• base
• more
• nonn

Comments

Each term is odd and next term is greater than 2500. Prime corresponding to the next term has more than 8900 digits. Number of digits of primes corresponding to the four known terms of this sequence are respectively 1,3,45 & 1881.

Next term is greater than 25000. - Michael S. Branicky, Sep 12 2024

Examples

			27 is in the sequence because 123456789101112131415161718192021222324252627 + 4 is a prime.
		

Crossrefs

Cf. A099081, A099082, A099083.

Extensions

a(5) from Michael S. Branicky, Jun 20 2023