login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A145121 Numbers n such that there exists x in N : (x+19)^3-x^3=n^2. 1

%I #15 Jan 03 2024 23:43:30

%S 361,108661,32815261,9910100161,2992817433361,903820954774861,

%T 272950935524574661,82430278707466772761,24893671218719440799161,

%U 7517806277774563654573861,2270352602216699504240506861,685638968063165475716978498161,207060698002473756967023265937761

%N Numbers n such that there exists x in N : (x+19)^3-x^3=n^2.

%H Vincenzo Librandi, <a href="/A145121/b145121.txt">Table of n, a(n) for n = 1..200</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (302,-1).

%F a(n+2) = 302*a(n+1)-a(n).

%F a(n) = 361*A145123(n). - _Colin Barker_, Oct 19 2014

%F G.f.: -361*x*(x-1) / (x^2-302*x+1). - _Colin Barker_, Oct 19 2014

%e a(1)=361 because 57^3-38^3=361^2.

%t CoefficientList[Series[361 (1 - x)/(x^2 - 302 x + 1), {x, 0, 20}], x] (* _Vincenzo Librandi_, Oct 19 2014

%o (PARI) Vec(-361*x*(x-1)/(x^2-302*x+1) + O(x^20)) \\ _Colin Barker_, Oct 19 2014

%o (Magma) I:=[361,108661]; [n le 2 select I[n] else 302*Self(n-1)-Self(n-2): n in [1..15]]; // _Vincenzo Librandi_, Oct 19 2014

%K easy,nonn

%O 1,1

%A _Richard Choulet_, Oct 02 2008

%E Editing and more terms from _Colin Barker_, Oct 19 2014

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 19 13:40 EDT 2024. Contains 371792 sequences. (Running on oeis4.)