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Search: id:A116889
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| A116889 |
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a(n) is the least prime p that remains prime through n iterations of function f(p)=p^2+4. |
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+0
4
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OFFSET
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0,1
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COMMENT
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The sequence is finite, since it can be proved that if p, f(p), f(f(p)), f(f(f(p))) and f(f(f(f(p)))) are all primes, then the next iteration gives a multiple of 13, greater than 13, thus a(k) for k>=5 does not exist.
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EXAMPLE
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a(0)=2 since f(2)=6 is not prime. a(1)=a(2)=3 since both f(3)=13 and f(f(3))=173 are primes.
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CROSSREFS
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Cf. A062324, A116886, A116887, A116888.
Sequence in context: A096502 A101462 A088266 this_sequence A037847 A037883 A023868
Adjacent sequences: A116886 A116887 A116888 this_sequence A116890 A116891 A116892
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KEYWORD
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fini,full,nonn
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AUTHOR
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Giovanni Resta (g.resta(AT)iit.cnr.it), Feb 27 2006
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