A086640 - OEIS

%I #10 Jun 17 2017 03:50:10

%S 7,30,71,130,207,302,415,546,695,862,1047,1250,1471,1710,1967,2242,

%T 2535,2846,3175,3522,3887,4270,4671,5090,5527,5982,6455,6946,7455,

%U 7982,8527,9090,9671,10270,10887,11522,12175,12846,13535,14242,14967,15710

%N Arrange n^2 octagons that each have area 7 so that they leave (n-1)^2 square gaps each with area 2; a(n) is the total area of these polygons.

%D Keith Devlin, "The language of mathematics", Henry Holt, NY, plate 9 after p. 249.

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

%F a(n) = 9n^2-4n+2.

%F G.f. -x*(2*x+7)*(1+x) / (x-1)^3 . - _R. J. Mathar_, Sep 15 2012

%o (PARI) a(n)=9*n^2-4*n+2 \\ _Charles R Greathouse IV_, Jun 17 2017

%K nonn,easy,less

%O 1,1

%A Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Jul 26 2003

%E Edited and extended by _David Wasserman_, Jun 20 2007