login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A158395 729n - 1. 2
728, 1457, 2186, 2915, 3644, 4373, 5102, 5831, 6560, 7289, 8018, 8747, 9476, 10205, 10934, 11663, 12392, 13121, 13850, 14579, 15308, 16037, 16766, 17495, 18224, 18953, 19682, 20411, 21140, 21869, 22598, 23327, 24056, 24785, 25514, 26243 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (729*n-1)^2-(729*n^2-2*n)*(27)^2=1 can be written as a(n)^2-A158394(n)*(27)^2=1.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Vincenzo Librandi, X^2-AY^2=1

E. J. Barbeau, Polynomial Excursions, Chapter 10: Diophantine equations (2010), pages 84-85 (row 15 in the first table at p. 85, case d(t) = t*(27^2*t-2)).

Index entries for linear recurrences with constant coefficients, signature (2,-1).

FORMULA

a(n) = 2*a(n-1)-a(n-2).

G.f.: x*(728+x)/(1-x)^2.

MATHEMATICA

LinearRecurrence[{2, -1}, {728, 1457}, 50]

PROG

(MAGMA) I:=[728, 1457]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];

(PARI) a(n) = 729*n - 1.

CROSSREFS

Cf. A158394.

Sequence in context: A191345 A023704 A043487 * A184077 A234652 A050219

Adjacent sequences:  A158392 A158393 A158394 * A158396 A158397 A158398

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Mar 18 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 10 19:08 EST 2016. Contains 279005 sequences.