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A165803
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Integers n such that repeated application of the map n->(n-3)/2 generates a chain of primes until either 3 or 2 is reached.
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1
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OFFSET
| 1,1
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COMMENTS
| For initial values n>3, the map is applied at least once, so 9 is in the sequence although it is not a prime. The sequence consists of p=2 and p=3 and the two finite chains of primes that are formed by repeated application of p->2*p+3, which are 2->7->17->37->77 and 3->9.
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EXAMPLE
| (77-3)/2=37(prime);(37-3)/2=17(prime);(17-3)/2=7(prime);(7-3)/2=2;no composite numbers smaller then 2 exists,end.
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MATHEMATICA
| f[n_]:=Module[{k=n}, While[k>3, k=(k-3)/2; If[ !PrimeQ[k], Break[]]]; PrimeQ[k]]; lst={}; Do[If[f[n], AppendTo[lst, n]], {n, 5!}]; lst
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CROSSREFS
| Cf. A165801, A165802
Sequence in context: A109660 A075855 A140189 * A204520 A007649 A046152
Adjacent sequences: A165800 A165801 A165802 * A165804 A165805 A165806
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KEYWORD
| nonn,fini,full,less
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AUTHOR
| Vladimir Orlovsky (4vladimir(AT)gmail.com), Sep 28 2009
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