0L systems, 82–85, 893
see also Substitution systems

√163
and almost integers, 915

17-gons
and constructible reals, 1129

1/f noise
in electronic systems, 969
and limits to randomization, 970
in radioactive decay, 970
and self-organized criticality, 989

1/f² noise, 1082
see also Random walks

1L systems, 85–88, 893
see also Substitution systems

1/n expansion, 1040

√2
continued fraction for, 144
digits of, 142
in musical chords, 917
and sine curves, 146
and substitution systems, 892, 904

2001: A Space Odyssey
extraterrestrial artifacts in, 1183
extraterrestrial contact in, 1190

21 cm line
on Pioneer 10 plaque, 1190
and water hole, 1189

24 dimensions
isotropy of lattices in, 980
sphere packing in, 987

2SAT (2-satisfiability problem), 1146

3
powers of, 119, 903

√3, and substitution systems, 904

3-regular graphs
see Networks, trivalent

3/2
powers of, 121, 903

3n+1 problem, 904
cellular automaton for, 904
as precursor to my work, 879
and register machines, 100
and Turing machine 600720, 1145
see also Arithmetic systems

3SAT (3-satisfiability problem), 1146

4-color theorem
see Four-Color Theorem

4 dimensions
isotropy of lattices in, 980
lattices in, 930
and spacetime, 481–486
see also Four-manifolds

411 services
name lookups in, 1100

5 dimensions
and Kaluza–Klein theory, 1028

5-fold symmetry
CA patterns with, 930

5/2
multiplication system, 123

5D hypercubes
and Penrose tilings, 932

60 (base)
of Babylonian numbers, 902

6j symbols
and spin networks, 1055

8 dimensions
isotropy of lattices in, 980
sphere packing in, 986