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A099070
Numbers n such that the concatenation of all nonprime natural numbers up to n with decreasing order is prime.
3
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
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
Sequence in context: A109602 A084991 A356824 * A288658 A065342 A231369
KEYWORD
base,more,nonn
AUTHOR
Farideh Firoozbakht, Nov 04 2004
STATUS
approved