%I #13 Sep 16 2019 00:58:26

%S 0,0,2,4,8,15,25,41,65,100,150,225,327,474,678,962,1348,1884,2602,

%T 3581,4889,6644,8968,12064,16124,21476,28462,37585,49407,64747,84495,

%U 109936,142522,184226,237350,304977,390669,499169,636039,808468,1024996,1296573,1636151

%N Number of simple graphs on n unlabeled nodes with maximum degree exactly 2.

%H Andrew Howroyd, <a href="/A324740/b324740.txt">Table of n, a(n) for n = 1..1000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/MaximumVertexDegree.html">Maximum Vertex Degree</a>

%F a(n) = A003292(n) - A008619(n).

%o (PARI) seq(n) = Vec( (1-x)*(1-x^2)/prod(k=1, n, 1 - x^k + O(x*x^n))^2 - 1/((1-x)*(1-x^2)), -n) \\ _Andrew Howroyd_, Sep 03 2019

%Y Column k=2 of A263293.

%Y A diagonal of A294217.

%Y Cf. A003292, A008619.

%K nonn

%O 1,3

%A _Andrew Howroyd_, Sep 03 2019