  The powers of 3 generate half of the odd residues mod 2^k (k>2), and a sign
change yields the other half. In other words: 3 is a semi-primitive root of 1
mod 2^k (k>2). Hence each k-bit residue is n = +/- 3^i.2^j mod 2^k, with unique
non-neg exponent pair: i<2^{k-2} and j<k. -- A new "dual base logarithmic"
binary number code (bases 2 and 3) employs this property. This (binary)
log-code [s,i,j] - where s is the corresponding sign, simplifies binary
multiplication by translating it to addition of the exponents of 2 and 3, and
XOR of the signs involved. -- Patent US-5923888 (13jul99)
