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

1, 1, 13, 239

Offset: 1

Author

Jonathan Sondow, Sep 30 2013

Keywords

• nonn
• fini
• full

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.

Examples

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

References

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

Links

• Wikipedia, Stella octangula number
• Wikipedia, Wilhelm Ljunggren

Crossrefs

Cf. A007588.