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 A071683 Nonprimes which are the average of two consecutive Fibonacci numbers. 0
 1, 4, 72, 305, 1292, 5473, 23184, 98209, 416020, 1762289, 7465176, 31622993, 133957148, 567451585, 2403763488, 10182505537, 43133785636, 182717648081, 774004377960, 3278735159921, 13888945017644, 58834515230497 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Prove that 17 is the only prime which is the average of two consecutive Fibonacci numbers. LINKS MATHEMATICA f[n_] := Fibonacci[n]; a = Select[ Range[70], IntegerQ[(f[ # ] + f[ # + 1])/2] && !PrimeQ[(f[ # ] + f[ # + 1])/2] &]; (f[a] + f[a + 1])/2 CROSSREFS Cf. A018252, A000045. Sequence in context: A077112 A203537 A095385 * A192826 A190398 A003752 Adjacent sequences:  A071680 A071681 A071682 * A071684 A071685 A071686 KEYWORD nonn AUTHOR G. L. Honaker, Jr., Jun 22 2002 EXTENSIONS Edited by Robert G. Wilson v, Jun 27 2002 STATUS approved

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Last modified August 22 20:47 EDT 2019. Contains 326209 sequences. (Running on oeis4.)