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A238329 Fibonacci numbers n that have no prime factors of the form 4k+1. 0
1, 1, 2, 3, 8, 21, 144, 987, 46368, 2178309, 4807526976 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

These are Fibonacci numbers of order 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, and 48. It is somewhat surprising that these are only these Fibonacci numbers having this property.

LINKS

Table of n, a(n) for n=1..11.

Florian Luca and Lawrence Somer, Lucas sequences for which 4 | phi(abs(u_n)) for almost all n, Fibonacci Quarterly, 44 (2006), pp. 249-262.

MATHEMATICA

Join[{1, 1}, Select[Fibonacci[Range[200]], Union[Mod[Transpose[FactorInteger[#]][[1]], 4]][[1]] > 1 &]]

CROSSREFS

Cf. A000045 (Fibonacci numbers).

Sequence in context: A004790 A245464 A243562 * A272333 A098119 A049959

Adjacent sequences:  A238326 A238327 A238328 * A238330 A238331 A238332

KEYWORD

nonn,fini,full

AUTHOR

T. D. Noe, Feb 26 2014

STATUS

approved

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Last modified December 17 00:23 EST 2018. Contains 318191 sequences. (Running on oeis4.)