%I A006772 M2971
%S A006772 1,3,14,70,370,2028,11452,66172,389416,2326202,14070268,86010680,530576780,
%T A006772 3298906810,20653559846,130099026600,823979294284,5244162058026,33523117491920,
               215150177410088
%N A006772 Sum of spans of n-step polygons on square lattice.
%D A006772 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A006772 A. J. Guttmann and I. G. Enting, The size and number of rings on the 
               square lattice, J. Phys. A 21 (1988), L165-L172.
%Y A006772 Sequence in context: A038213 A161939 A001579 this_sequence A009020 A109792 
               A137177
%Y A006772 Adjacent sequences: A006769 A006770 A006771 this_sequence A006773 A006774 
               A006775
%K A006772 nonn
%O A006772 1,2
%A A006772 N. J. A. Sloane (njas(AT)research.att.com).