A071683 Nonprimes which are the average of two consecutive Fibonacci numbers.

1, 4, 72, 305, 1292, 5473, 23184, 98209, 416020, 1762289, 7465176, 31622993, 133957148, 567451585, 2403763488, 10182505537, 43133785636, 182717648081, 774004377960, 3278735159921, 13888945017644, 58834515230497

Offset

1,2

Comments

Prove that 17 is the only prime which is the average of two consecutive Fibonacci numbers.

Links

Table of n, a(n) for n=1..22.

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