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 A053409 #32 Jun 26 2020 19:01:45
%S A053409 21,34,55,377,4181,17711,121393,1346269,5702887,165580141,53316291173,
%T A053409 956722026041,2504730781961,308061521170129,806515533049393,
%U A053409 14472334024676221,1779979416004714189,19740274219868223167,573147844013817084101,10284720757613717413913
%N A053409 Fibonacci numbers which are semiprimes.
%C A053409 Subsequence of A006881, since the only square Fibonacci numbers are 1 and 144. - _Charles R Greathouse IV_, Sep 24 2012
%C A053409 Apart from a(1) = 21, all terms are of the form F(p), F(2p), or F(p^2) where F(n) is the n-th Fibonacci number. - _Charles R Greathouse IV_, Oct 06 2016
%H A053409 Vincenzo Librandi, <a href="/A053409/b053409.txt">Table of n, a(n) for n = 1..48</a>
%F A053409 a(n) = A000045(A072381(n)).
%t A053409 Select[Fibonacci@Range[120],Last/@FactorInteger[#]=={1,1}&] (* _Vladimir Joseph Stephan Orlovsky_, Jan 29 2012 *)
%t A053409 Select[Fibonacci[Range[150]],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Jun 26 2020 *)
%o A053409 (PARI) issemi(n)=bigomega(n)==2
%o A053409 list(lim)=my(v=List([21]),F,t); forprime(p=2,, F=fibonacci(p); if(F>lim, break); if(issemi(F), listput(v,F))); forprime(p=2,, F=fibonacci(p^2); if(F>lim, break); if(isprime(t=fibonacci(p)) && isprime(F/t), listput(v,F))); forprime(p=2,, F=fibonacci(2*p); if(F>lim, break); if(isprime(t=fibonacci(p)) && isprime(F/t), listput(v,F))); Set(v) \\ _Charles R Greathouse IV_, Oct 06 2016
%Y A053409 Cf. A000045, A001358, A006881, A072381.
%Y A053409 Column k=2 of A303216.
%K A053409 nonn
%O A053409 1,1
%A A053409 _G. L. Honaker, Jr._, Jan 09 2000