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 A080121 a(n) = smallest k>0 such that n^2^k + (n+1)^2^k is prime, or -1 if no such k exists. 5
 1, 1, 2, 1, 1, 2, 1, 2, 1, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS This sequence is log2 of A077659. It is known that a(11) > 22. Is it possible that 11^2^k + 12^2^k is composite for all k > 0? The corresponding primes are listed in A122900. Currently a(n) is unknown for n in {11,15,18,20,28,44,46,49,51,52,53,55,57,58,61,62,64,71,73,77,81,83,91,92,94,...}. All n<100 and 0 0, then a(n) = A058064(n). - Max Alekseyev, Sep 10 2020 CROSSREFS Cf. A058064, A057856, A077659, A122900, A122902. Sequence in context: A131374 A207409 A013632 * A122901 A001917 A240545 Adjacent sequences:  A080118 A080119 A080120 * A080122 A080123 A080124 KEYWORD hard,more,nonn AUTHOR T. D. Noe, Jan 29 2003 EXTENSIONS Edited by Max Alekseyev, Sep 09 2020 STATUS approved

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Last modified April 15 10:46 EDT 2021. Contains 342977 sequences. (Running on oeis4.)