%I #29 Jun 17 2017 03:37:18

%S 0,4,28,72,136,220,324,448,592,756,940,1144,1368,1612,1876,2160,2464,

%T 2788,3132,3496,3880,4284,4708,5152,5616,6100,6604,7128,7672,8236,

%U 8820,9424,10048,10692,11356,12040,12744,13468,14212,14976,15760

%N 4 times heptagonal numbers: 2n(5n-3).

%C Sequence found by reading the line from 0, in the direction 0, 4,..., in the square spiral whose vertices are the generalized heptagonal numbers A085787. - _Omar E. Pol_, Jul 18 2012

%H Ivan Panchenko, <a href="/A153784/b153784.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F a(n) = 10n^2 - 6n = A000566(n)*4 = A135706(n)*2.

%F a(n)=20*n+a(n-1)-16 (with a(0)=0) - _Vincenzo Librandi_, Aug 03 2010

%F a(n) = A087348(n) - 1, n >= 1. - _Omar E. Pol_, Jul 18 2012

%F a(0)=0, a(1)=4, a(2)=28, a(n)=3*a(n-1)-3*a(n-2)+a(n-3). - _Harvey P. Dale_, Mar 19 2015

%t s=0;lst={s};Do[s+=n;AppendTo[lst,s],{n,4,6!,20}];lst (* _Vladimir Joseph Stephan Orlovsky_, Apr 02 2009 *)

%t Table[2n(5n-3),{n,0,40}] (* or *) LinearRecurrence[{3,-3,1},{0,4,28},50] (* _Harvey P. Dale_, Mar 19 2015 *)

%o (PARI) a(n)=2*n*(5*n-3) \\ _Charles R Greathouse IV_, Jun 17 2017

%Y Cf. A000566, A135706, A152773, A152785.

%K easy,nonn

%O 0,2

%A _Omar E. Pol_, Jan 02 2009