%I A016028
%S A016028 1,2,3,4,6,9,13,18,24,31,39,48,58,69,81,94,108,123,139,156,174,193,
%T A016028 213,234,256,279,303,328,354,381,409,438,468,499,531,564,598,633,
%U A016028 669,706,744,783,823,864,906,949,993,1038,1084,1131,1179
%N A016028 Expansion of (1 - x + x^4) / (1 - x)^5.
%C A016028 For n>2, maximal number of edges in critical strongly connected digraphs 
               on n-1 vertices.
%C A016028 If Y is a 3-subset of an n-set X then, for n>=3, a(n) is the number of 
               2-subsets of X which have no exactly one element in common with Y. 
               Also, if Y is a 3-subset of an n-set X then, for n>=4, a(n-3) is 
               the number of (n-2)-subsets of X which have no exactly two elements 
               in common with Y. - Milan R. Janjic (agnus(AT)blic.net), Dec 28 2007
%H A016028 R. Aharoni and E. Berger, <a href="http://arXiv.org/abs/math.CO/9911113">
               [math/9911113] The number of edges in critical strongly connected 
               graphs</a>
%F A016028 Also, from the third term on, triangular numbers + 3 - Alexandre Wajnberg 
               (alexandre.wajnberg(AT)skynet.be), Dec 10 2005
%F A016028 a(n)=binomial(n,2)-3*n+9, n=3,4,5,.... a(n-3)=n^2/2-7*n/2+9, n=4,5,6,
               .... - Milan R. Janjic (agnus(AT)blic.net), Dec 28 2007
%t A016028 i=0;s=3;lst={1, 2};Do[s+=n+i;AppendTo[lst, s], {n, 0, 6!, 1}];lst [From 
               Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 30 2008]
%Y A016028 Essentially triangular numbers (A000217) plus 3. Cf. A000124.
%Y A016028 Sequence in context: A097557 A123648 A129632 this_sequence A098578 A076968 
               A098889
%Y A016028 Adjacent sequences: A016025 A016026 A016027 this_sequence A016029 A016030 
               A016031
%K A016028 nonn
%O A016028 1,2
%A A016028 Robert G. Wilson v (rgwv(AT)rgwv.com)