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%I #19 Jul 21 2023 17:19:55
%S 1,3,21,55
%N Positive Fibonacci numbers that are also triangular numbers.
%C Vern Hoggatt conjectured and Luo Ming confirmed that these are all the terms. - _Tomohiro Yamada_, Sep 23 2017
%D J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 55, p. 20, Ellipses, Paris 2008.
%D D. Wells, Curious and interesting numbers, Penguin Books, p. 108
%H Luo Ming, <a href="http://www.fq.math.ca/Scanned/27-2/ming.pdf">On triangular Fibonacci numbers</a>, Fibonacci Quart. 27 (1989), 98--108.
%t Union[Select[Fibonacci[Range[20]],OddQ[Sqrt[8#+1]]&]] (* _Harvey P. Dale_, Jan 17 2015 *)
%Y Cf. A000045, A000217.
%K nonn,fini,full
%O 1,2
%A _Felice Russo_
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