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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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4
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OFFSET
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0,1
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COMMENTS
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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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LINKS
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EXAMPLE
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a(0)=2 since f(2)=8 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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KEYWORD
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fini,full,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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