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 A114974 Numbers n such that 7^n + n^7 is a semiprime. 4
 2, 12, 16, 18, 30, 39, 160, 214, 235, 408 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 627 and 748 are sequence terms < 1100. a(11) >= 510. Unknown factorization also for 622 and 790. - Hugo Pfoertner, Jul 28 2019 LINKS Table of n, a(n) for n=1..10. Status of 7^510-510^7 in factordb.com. EXAMPLE 2 is in the sequence because 7^2 + 2^7 = 177 = 3*59 (semiprime). 12 is in the sequence because 7^12 + 12^7 = 13*1067470693 (semiprime). [Vincenzo Librandi, Dec 16 2010] PROG (Magma)IsSemiprime:=func; [n: n in [1..85] | IsSemiprime(7^n+n^7)] // Vincenzo Librandi, Dec 16 2010 CROSSREFS Cf. A114970, A114971, A114973. Sequence in context: A120300 A089021 A176888 * A298001 A071566 A295821 Adjacent sequences: A114971 A114972 A114973 * A114975 A114976 A114977 KEYWORD nonn,more,hard AUTHOR Zak Seidov, Feb 22 2006 EXTENSIONS Corrected (inserted 12) from Vincenzo Librandi, Dec 16 2010 a(7) from D. S. McNeil, Dec 16 2010 a(8)-a(10) from Luke March, Aug 03 2015 STATUS approved

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Last modified June 9 09:14 EDT 2023. Contains 363177 sequences. (Running on oeis4.)