A083750 Numbers n such that 2111131111...p(n-1)1111p(n) is prime.

85, 145, 304, 915

Offset

1,1

Comments

Let fp(n,k) be the decimal concatenation of prime(n), k, and fp(n-1,k) for n > 1, and fp(1,k) = 2. Then a(n) = fp(n, 1111).

No more terms up to 6300.

Links

Table of n, a(n) for n=1..4.

Farideh Firoozbakht, On Solution of puzzle 208 .

Example

a(1)=85 because fp(85,1111)= 211113111151111...4331111439 is prime and fp(k,1111) is composite for k< 85 (prime(85)=439).
a(3)=304 because fp(304,1111)=211113111151111...199911112003 is a prime related to prime year 2003; this prime number has 2231 digits. fp(915,1111)=211113111151111...712911117151 is a prime with 7119 digits (prime(915)=7151).

Crossrefs

Cf. A083677, A082549.

Sequence in context: A273123 A239527 A029471 * A043684 A043574 A043739

Adjacent sequences: A083747 A083748 A083749 * A083751 A083752 A083753

Keyword

nonn,base

Author

Farideh Firoozbakht, Jun 17 2003

Extensions

Comment from Charles R Greathouse IV, Oct 12 2009

Status

approved