%I #9 Aug 13 2020 14:01:06

%S 224,705,1600,3065,5280,8449,12800,18585,26080,35585,47424,61945,

%T 79520,100545,125440,154649,188640,227905,272960,324345,382624,448385,

%U 522240,604825,696800,798849,911680,1036025,1172640,1322305,1485824,1664025

%N Surround numbers of an n X 2 rectangle when n is even.

%C See A061525 for odd n.

%H E. J. Friedman, <a href="https://erich-friedman.github.io/mathmagic/0599.html">Math. Magic: May, 1999</a>

%F a(n) = (n^4 + 32n^3 + 344n^2 + 768n + 400)/16 for even n.

%F From _Chai Wah Wu_, Dec 20 2019: (Start)

%F a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n > 6.

%F G.f.: x^2*(-25*x^4 + 125*x^3 - 315*x^2 + 415*x - 224)/(x - 1)^5. (End)

%Y Cf. A047875 A061525.

%K easy,nonn

%O 2,1

%A _Jason Earls_, May 03 2001

%E More terms from Larry Reeves (larryr(AT)acm.org), May 07 2001