A039595 Positive Fibonacci numbers that are also triangular numbers.

1, 3, 21, 55

Offset

1,2

Comments

Vern Hoggatt conjectured and Luo Ming confirmed that these are all the terms. - Tomohiro Yamada, Sep 23 2017

References

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 55, p. 20, Ellipses, Paris 2008.

D. Wells, Curious and interesting numbers, Penguin Books, p. 108

Links

Table of n, a(n) for n=1..4.

Luo Ming, On triangular Fibonacci numbers, Fibonacci Quart. 27 (1989), 98--108.

Mathematica

Union[Select[Fibonacci[Range[20]], OddQ[Sqrt[8#+1]]&]] (* Harvey P. Dale, Jan 17 2015 *)

Crossrefs

Cf. A000045, A000217.

Sequence in context: A303834 A340687 A152773 * A033567 A181156 A356809

Adjacent sequences: A039592 A039593 A039594 * A039596 A039597 A039598

Keyword

nonn,fini,full

Author

Felice Russo

Status

approved