

A075848


2*n^2 + 9 is a square.


5



0, 6, 36, 210, 1224, 7134, 41580, 242346, 1412496, 8232630, 47983284, 279667074, 1630019160, 9500447886, 55372668156, 322735561050, 1881040698144, 10963508627814, 63900011068740, 372436557784626, 2170719335639016
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OFFSET

0,2


COMMENTS

Lim. n> Inf. a(n)/a(n1) = 3 + 2*Sqrt(2).


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. 248268, 1966.
L. E. Dickson, History of the Theory of Numbers, Vol. II, Diophantine Analysis. AMS Chelsea Publishing, Providence, Rhode Island, 1999, pp. 341400.
Peter G. L. Dirichlet, Lectures on Number Theory (History of Mathematics Source Series, V. 16); American Mathematical Society, Providence, Rhode Island, 1999, pp. 139147.


LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000
Tanya Khovanova, Recursive Sequences
J. J. O'Connor and E. F. Robertson, Pell's Equation
Eric Weisstein's World of Mathematics, Pell Equation.
Index entries for linear recurrences with constant coefficients, signature (6,1).


FORMULA

a(n) = [(3+2*Sqrt(2))^n  (32*Sqrt(2))^n] * [3/(2*Sqrt(2))]; a(n) = 6*a(n1)  a(n2).
a(n) = 6*A001109(n).
G.f.: 6x/(16x+x^2). [From Philippe Deléham, Nov 17 2008]


MATHEMATICA

LinearRecurrence[{6, 1}, {0, 6}, 30] (* Harvey P. Dale, Nov 28 2012 *)


CROSSREFS

Sequence in context: A269406 A269603 A027910 * A096979 A269464 A123887
Adjacent sequences: A075845 A075846 A075847 * A075849 A075850 A075851


KEYWORD

nonn,easy


AUTHOR

Gregory V. Richardson, Oct 15 2002


STATUS

approved



