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 A116889 a(n) is the least prime p that remains prime through n iterations of function f(p)=p^2+4. 4
 2, 3, 3, 5087, 306167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS 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. LINKS EXAMPLE 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. CROSSREFS Cf. A062324, A116886, A116887, A116888. Sequence in context: A323340 A280895 A088266 * A347716 A037847 A037883 Adjacent sequences:  A116886 A116887 A116888 * A116890 A116891 A116892 KEYWORD fini,full,nonn AUTHOR Giovanni Resta, Feb 27 2006 EXTENSIONS Typo in Example fixed by Zak Seidov, Nov 07 2013 STATUS approved

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Last modified October 6 16:34 EDT 2022. Contains 357270 sequences. (Running on oeis4.)