OFFSET
0,3
COMMENTS
Equivalently, lattice points where the gcd of all the coordinates is 1.
LINKS
Index entries for linear recurrences with constant coefficients, signature (18,-115,330,-424,192).
FORMULA
a(n) = 8^n - 4^n - 3^n - 2^n + 2.
G.f.: -x*(200*x^3-136*x^2+19*x+1)/((x-1)*(2*x-1)*(3*x-1)*(4*x-1)*(8*x-1)). - Colin Barker, Sep 04 2012
EXAMPLE
a(2) = 37 because in 2D the lines have slope 0, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7, 1/6, 5/6, 1/5, 2/5, 3/5, 4/5, 1/4, 3/4, 1/3, 2/3, 1/2, 1 and their reciprocals.
MATHEMATICA
Table[8^n - 4^n - 3^n - 2^n + 2, {n, 0, 20}]
PROG
(Python)
[8**n-4**n-3**n-2**n+2 for n in range(25)] # Gennady Eremin, Mar 09 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Joshua Zucker, Nov 20 2003
STATUS
approved