This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A139095 #25 Jun 28 2025 22:37:42
%S A139095 1,1,2,3,5,13,89,233,1597,28657,514229,433494437,2971215073,
%T A139095 99194853094755497,1066340417491710595814572169,
%U A139095 19134702400093278081449423917,475420437734698220747368027166749382927701417016557193662268716376935476241
%N A139095 Fibonacci numbers whose sum of proper divisors is also a Fibonacci number.
%C A139095 Fibonacci numbers k such that A001065(k) is a Fibonacci number.
%C A139095 A001065(a(n)) is a Fibonacci number.
%C A139095 Certainly this contains 1 and the terms of A005478. Does it contain any other terms? - _R. J. Mathar_, Sep 17 2009
%C A139095 The next term, Fibonacci(359) = 4.754...*10^74, is too large to include in the data section. There are no composite Fibonacci numbers below A000045(1423) in this sequence. - _Amiram Eldar_, Mar 11 2024
%p A139095 isA000045 := proc(n) local i,f ; for i from 0 do f := combinat[fibonacci](i) ; if f = n then RETURN(true) ; elif f > n then RETURN(false) ; fi ; od; end: A001065 := proc(n) numtheory[sigma](n)-n ; end: isA139095 := proc(n) RETURN( isA000045(n) and isA000045(A001065(n)) ) ; end: for i from 1 to 230 do if isA139095(combinat[fibonacci](i)) then printf("%d,", combinat[fibonacci](i)) ; fi ; od: # _R. J. Mathar_, May 22 2008
%t A139095 Fsum[n_]:=DivisorSigma[1,n]-n;Select[Fibonacci[Range[140]],IntegerQ[Sqrt[5*Fsum[#]^2 + 4]] || IntegerQ[Sqrt[5*Fsum[#]^2 - 4]]&] (* _James C. McMahon_, Jun 28 2025 *)
%Y A139095 Cf. A000045, A001065, A005478, A074283, A139589.
%K A139095 nonn
%O A139095 1,3
%A A139095 _Omar E. Pol_, May 11 2008
%E A139095 More terms from _R. J. Mathar_, May 22 2008