%I A031878
%S A031878 0,1,3,5,10,13,21,25,36,41,55,61,78,85,105,113,136,145,171,181,210,221,
%T A031878 253,265,300,313,351,365,406,421,465,481,528,545,595,613,666,685,741,
%U A031878 761,820,841,903,925,990,1013,1081,1105,1176,1201,1275,1301,1378
%N A031878 Maximal number of edges in Hamiltonian path in complete graph on n nodes.
%F A031878 C(n, 2) if n odd, C(n, 2)-n/2+1 if n even; G.f.: x^2*(1+2*x+x^3)/((1-x)*(1-x^2)).
%F A031878 a(n)= ( n*n +n -(n-1)*(n mod 2) )/2, (frank.ellermann(AT)t-online.de).
%e A031878 E.g. for n=4 [1:2][2:3][3:1][1:4][4:2], so a(4) = 5.
%Y A031878 Cf. A031940.
%Y A031878 Sequence in context: A034746 A080931 A165718 this_sequence A160792 A137395 
               A001767
%Y A031878 Adjacent sequences: A031875 A031876 A031877 this_sequence A031879 A031880 
               A031881
%K A031878 nonn
%O A031878 1,3
%A A031878 Colin L. Mallows (colinm(AT)research.avayalabs.com)