A229384 Positive integer solutions y1, x1, y2, x2 to Ljunggren's equation x^2 + 1 = 2y^4.

1, 1, 13, 239

Offset

1,3

Comments

See the Wikipedia links for other references.

The only square stella octangula numbers are A007588(1) = (a(1)*a(2))^2 = 1 and A007588(169) = (a(3)*a(4))^2 = 9653449.

References

W. Ljunggren, Zur Theorie der Gleichung x^2 + 1 = Dy^4, Avh. Norske Vid. Akad. Oslo. I. 1942 (5): 27.

Links

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

Wikipedia, Stella octangula number

Wikipedia, Wilhelm Ljunggren

Example

239^2 + 1 = 57122 = 2*13^4.

Crossrefs

Cf. A007588.

Sequence in context: A134493 A051689 A000824 * A181035 A228795 A271782

Adjacent sequences: A229381 A229382 A229383 * A229385 A229386 A229387

Keyword

nonn,fini,full

Author

Jonathan Sondow, Sep 30 2013

Status

approved