OFFSET
0,2
COMMENTS
Appears to be the coordination sequence for a tetravalent node in the bex tiling (or net).
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Reticular Chemistry Structure Resource (RCSR), The bex tiling (or net)
Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1).
FORMULA
a(0)=1; thereafter, a(3*k) = 10*k, a(3*k+1) = 10*k+4, a(3*k+2) = 10*k+6.
a(n) = a(n-1) + a(n-3) - a(n-4) for n>4. - Colin Barker, Jan 27 2018
MAPLE
f4:=proc(n)
if n=0 then 1
elif (n mod 3) = 0 then 10*n/3
elif (n mod 3) = 1 then (10*n+2)/3
else (10*n-2)/3; fi; end;
[seq(f4(n), n=0..80)];
PROG
(PARI) Vec((1 + x^2)*(1 + 3*x + x^2) / ((1 - x)^2*(1 + x + x^2)) + O(x^100)) \\ Colin Barker, Jan 27 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jan 26 2018
STATUS
approved