A099070 Numbers n such that the concatenation of all nonprime natural numbers up to n with decreasing order is prime.

4, 5, 6, 7, 8, 9, 26, 1752, 1753

Offset

1,1

Comments

If n is in the sequence and n+1 is prime then n+1 is also in the sequence. Next term is greater than 5450 and the prime corresponding to the next term has more than 18000 digits. Number of digits of primes corresponding to the nine known terms of the sequence are respectively 2,2,3,3,4,5,29,5010 & 5010.

Links

Table of n, a(n) for n=1..9.

Carlos Rivera, Puzzle 8. Primes by Listing, The Prime Puzzles & Problems connection.

Example

9 is in the sequence because all nonprime natural numbers up to 9 are 1,4,6,8 & 9 and 98641 is prime.

Mathematica

Do[If[PrimeQ[(v={}; Do[If[ !PrimeQ[n+1-j], v=Join[v, IntegerDigits [n+1-j]]], {j, n}]; FromDigits[v])], Print[n]], {n, 5450}]

Crossrefs

Cf. A046284, A099071.

Sequence in context: A109602 A084991 A356824 * A288658 A065342 A231369

Adjacent sequences: A099067 A099068 A099069 * A099071 A099072 A099073

Keyword

base,more,nonn

Author

Farideh Firoozbakht, Nov 04 2004

Status

approved