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

1,2

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

Links

Table of n, a(n) for n=1..5.

Example

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

Crossrefs

Cf. A099081, A099082, A099083.

Sequence in context: A219345 A185037 A185237 * A085656 A113100 A038379

Adjacent sequences: A099081 A099082 A099083 * A099085 A099086 A099087

Keyword

base,more,nonn

Author

Farideh Firoozbakht, Nov 03 2004

Extensions

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

Status

approved