%I #28 Aug 14 2021 07:14:39
%S 1,2,4,11,33,151,988,11453,247357,10608128,901029366,148187993520
%N Number of distinct characteristic polynomials among all simple undirected graphs on n nodes.
%H Andries E. Brouwer, <a href="http://www.win.tue.nl/~aeb/graphs/cospectral/cospectralA.html">Numbers of characteristic polynomials and cospectral graphs for A</a>
%H A. E. Brouwer and E. Spence, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v16i1n20">Cospectral graphs on 12 vertices</a>, Electr. J. Combin. 16 (2009) N20. (p. 199).
%H Lorentz Jäntschi and Sorana D. Bolboacă, <a href="https://doi.org/10.1201/9780429022944-7">Characteristic Polynomial</a>, Chapter 7, New Frontiers in Nanochemistry, 1st ed., Apple Academic Press, 2020.
%H Dan-Marian Joiţa and Lorentz Jäntschi, <a href="https://doi.org/10.3390/math5040084">Extending the Characteristic Polynomial for Characterization of C_20 Fullerene Congeners</a>, Mathematics (2017), 5(4), 84.
%H E. Spence, <a href="http://www.maths.gla.ac.uk/~es/cospec/cospec.html"> Numbers of characteristic polynomials and cospectral graphs for A</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CharacteristicPolynomial.html">Characteristic Polynomial</a>
%Y Cf. A000088.
%K nonn,hard,more
%O 1,2
%A _Eric W. Weisstein_, Apr 03 2003
%E One term added by _Andries E. Brouwer_, Apr 09 2009
%E Two more terms from _Ruperto Corso_, Dec 18 2011