OFFSET
1,3
LINKS
Stephan Brandt, Janina Müttel, Dieter Rautenbach, The circumference of the square of a connected graph, Combinatorica 34 (2014), no. 5, 547--559. MR3276436.
FORMULA
See Maple code.
Conjectures from Colin Barker, Feb 21 2015: (Start)
a(n) = a(n-1)+3*a(n-3)-3*a(n-4) for n>10.
G.f.: -x^2*(x^8-x^7+x^6-x^5+x^4+x^3-x^2-x-1) / ((x-1)*(3*x^3-1)).
(End)
MAPLE
f:=proc(k, i)
if i=1 then (23*3^k-1)/2
elif i=2 then (33*3^k-1)/2
else (47*3^k-1)/2; fi;
end;
g:=proc(n) local r, s;
s := (n mod 3); if s=0 then s:=s+3; fi; r:=(n-s)/3;
f(r-2, s);
end;
a:=[0, 1, 2, 3, 5, 7, 11, 16, 23];
for n from 10 to 50 do a:=[op(a), g(n)]; od;
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 21 2015
STATUS
approved