This site is supported by donations to The OEIS Foundation.

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!)
 A007518 Floor(n*(n+2)*(2*n-1)/8). (Formerly M2776) 2

%I M2776

%S 0,3,9,21,39,66,102,150,210,285,375,483,609,756,924,1116,1332,1575,

%T 1845,2145,2475,2838,3234,3666,4134,4641,5187,5775,6405,7080,7800,

%U 8568,9384,10251,11169,12141,13167,14250,15390

%N Floor(n*(n+2)*(2*n-1)/8).

%D From a problem on p. 151 of J. Rec. Math., 7 (1975).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (3, -2, -2, 3, -1).

%F a(n) = 3*A002623(n) for n>0. - _M. F. Hasler_, Sep 15 2009

%F G.f.: 3*x/((x+1)*(x-1)^4) [Maksym Voznyy (voznyy(AT)mail.ru), Aug 10 2009]

%F a(1)=0, a(2)=3, a(3)=9, a(4)=21, a(5)=39, a(n)=3*a(n-1)-2*a(n-2)- 2*a(n-3)+ 3*a(n-4)-a (n-5). - _Harvey P. Dale_, Oct 06 2014

%t Table[Floor[(n(n+2)(2n-1))/8],{n,50}] (* or *) LinearRecurrence[{3,-2,-2,3,-1},{0,3,9,21,39},40] (* _Harvey P. Dale_, Oct 06 2014 *)

%o (PARI) vector(50, n, n*(n+2)*(2*n-1)\8) \\ _Michel Marcus_, Oct 12 2014

%Y Column 4 of triangle A094953.

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_, _Robert G. Wilson v_

%E Offset corrected by _Harvey P. Dale_, Oct 06 2014

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.