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A075870 2*n^2 - 4 is a square. +0
2
2, 10, 58, 338, 1970, 11482, 66922, 390050, 2273378, 13250218, 77227930, 450117362, 2623476242, 15290740090, 89120964298, 519435045698, 3027489309890, 17645500813642, 102845515571962, 599427592618130 (list; graph; listen)
OFFSET

1,1

COMMENT

Lim. n-> Inf. a(n)/a(n-1) = 3 + 2*Sqrt(2).

Also gives solutions to the equation x^2-2 = floor(x*r*floor(x/r)) where r=sqrt(2) - Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 14 2004

REFERENCES

A. H. Beiler, "The Pellian", ch. 22 in Recreations in the Theory of Numbers: The Queen of Mathematics Entertains. Dover, New York, New York, pp. 248-268, 1966.

L. E. Dickson, History of the Theory of Numbers, Vol. II, Diophantine Analysis. AMS Chelsea Publishing, Providence, Rhode Island, 1999, p. 341-400.

Peter G. L. Dirichlet, Lectures on Number Theory (History of Mathematics Source Series, V. 16); American Mathematical Society, Providence, Rhode Island, 1999, p. 139-147.

LINKS

Tanya Khovanova, Recursive Sequences

J. J. O'Connor and E. F. Robertson, Pell's Equation

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

FORMULA

a(n) = 1/sqrt(2)*((1+sqrt(2))^(2*n-1)-(1-sqrt(2))^(2*n-1)) = 6*a(n-1) - a(n-2)

CROSSREFS

Cf. 2*A001653.

Adjacent sequences: A075867 A075868 A075869 this_sequence A075871 A075872 A075873

Sequence in context: A000172 A097971 A093303 this_sequence A074608 A086871 A108450

KEYWORD

nonn

AUTHOR

Gregory V. Richardson (omomom(AT)hotmail.com), Oct 16 2002

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Last modified May 16 23:01 EDT 2008. Contains 139884 sequences.


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