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A139590 Fibonacci numbers with a non-Fibonacci number of divisors. 3
8, 21, 34, 55, 144, 377, 2584, 4181, 6765, 17711, 46368, 75025, 121393, 196418, 317811, 832040, 1346269, 2178309, 5702887, 14930352, 102334155, 165580141, 267914296, 701408733, 1134903170, 4807526976, 12586269025, 32951280099 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A000005(a(n)) is a non-Fibonacci number A001690.

LINKS

Table of n, a(n) for n=1..28.

EXAMPLE

34 belongs to the sequence because the number of its divisors, 4, is not a Fibonacci number.

MAPLE

A000045 := proc(n) option remember ; coeftayl( x/(1-x-x^2), x=0, n) ; end: isA000045 := proc(n) local a; for a from 0 do if A000045(a) > n then RETURN(false) ; elif A000045(a)=n then RETURN(true) ; fi ; od: end: A000005 := proc(n) numtheory[tau](n) ; end: isA139590 := proc(n) RETURN(isA000045(n) and not isA000045(A000005(n))) ; end: for i from 1 to 130 do a000045 := A000045(i) ; if isA139590(a000045) then printf("%d, ", a000045) ; fi ; od: # R. J. Mathar, May 11 2008

with(combinat): with(numtheory): F:={seq(fibonacci(j), j=1..30)}: a:= proc(n) if member(tau(fibonacci(n)), F) = false then fibonacci(n) else end if end proc: seq(a(n), n=1..50); # Emeric Deutsch

MATHEMATICA

With[{fibs=Fibonacci[Range[60]]}, Transpose[Select[Thread[{fibs, DivisorSigma[ 0, fibs]}], !MemberQ[ fibs, #[[2]]]&]][[1]]] (* Harvey P. Dale, Aug 04 2013 *)

CROSSREFS

Cf. A000005, A000045, A001690, A063375, A133021.

Sequence in context: A134862 A302253 A090206 * A154894 A241986 A179681

Adjacent sequences:  A139587 A139588 A139589 * A139591 A139592 A139593

KEYWORD

nonn

AUTHOR

Omar E. Pol, May 09 2008

EXTENSIONS

More terms from R. J. Mathar and Emeric Deutsch, May 11 2008

STATUS

approved

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Last modified January 28 00:32 EST 2020. Contains 331313 sequences. (Running on oeis4.)