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A039595 Fibonacci numbers that are also triangular numbers. 4
1, 3, 21, 55 (list; graph; refs; listen; history; text; internal format)
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: A219069 A027499 A152773 * A033567 A181156 A162394

Adjacent sequences:  A039592 A039593 A039594 * A039596 A039597 A039598

KEYWORD

nonn,fini,full

AUTHOR

Felice Russo

STATUS

approved

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Last modified February 20 15:02 EST 2018. Contains 299380 sequences. (Running on oeis4.)