# Index

See page 852 for notes about this index and about entries for personal names.

See the Names Index for personal names only.

Note that names mentioned only in the Preface are not included in this index.

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/f ^{2}* 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`

, and substitution systems, 904

3-regular graphs

see Networks, trivalent

*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