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A068717 a(n) = -1 if A067280(n) = 0 mod 2, otherwise a(n) = A049240(n). 3
0, -1, 1, 0, -1, 1, 1, 1, 0, -1, 1, 1, -1, 1, 1, 0, -1, 1, 1, 1, 1, 1, 1, 1, 0, -1, 1, 1, -1, 1, 1, 1, 1, 1, 1, 0, -1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 1, 1, 0, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, 1, 1, 0, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, 1, 1, 0, -1, 1, 1, -1, 1, 1, 1, -1, 1, 1, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Previous name was: x*x - n*y*y = +-1 has infinitely many solutions in integers (x,y).

REFERENCES

H. Davenport, The Higher Arithmetic. Cambridge Univ. Press, 7th ed., 1999, table 1.

LINKS

Table of n, a(n) for n=1..94.

John Robertson, Solving the generalized Pell equation x^2-dy^2=N.

FORMULA

a(n) = -1 if A067280(n) = 0 mod 2, otherwise a(n) = A049240(n).

EXAMPLE

a(2)= -1: x*x -2*y*y = -1 is soluble, e.g. 7*7 -2*5*5 = -1.

CROSSREFS

Cf. A068716, A068718, A067280, A049240, A006702, A006703.

Sequence in context: A332814 A285418 A344617 * A049240 A285978 A138712

Adjacent sequences:  A068714 A068715 A068716 * A068718 A068719 A068720

KEYWORD

sign,easy

AUTHOR

Frank Ellermann, Feb 25 2002

EXTENSIONS

New name from formula by Joerg Arndt, Aug 29 2020

STATUS

approved

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Last modified September 25 16:17 EDT 2021. Contains 347658 sequences. (Running on oeis4.)