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A083750 Numbers n such that 2111131111...p(n-1)1111p(n) is prime. 0

%I #7 Mar 31 2012 14:40:08

%S 85,145,304,915

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

%C 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).

%C No more terms up to 6300.

%H Farideh Firoozbakht, <a href="http://www.primepuzzles.net/puzzles/puzz_208.htm">On Solution of puzzle 208 </a>.

%e a(1)=85 because fp(85,1111)= 211113111151111...4331111439 is prime and fp(k,1111) is composite for k< 85 (prime(85)=439).

%e 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).

%Y Cf. A083677, A082549.

%K nonn,base

%O 1,1

%A _Farideh Firoozbakht_, Jun 17 2003

%E Comment from _Charles R Greathouse IV_, Oct 12 2009

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Last modified March 28 17:25 EDT 2024. Contains 371254 sequences. (Running on oeis4.)