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The phi numeral system (golden ratio base, golden section base, golden mean base, ϕ base, base ϕ, phinary, phigital) uses the the golden ratio (symbolized by the Greek letter ϕ) as the base for a noninteger base positional numeral system. Although it is an irrational base, it is not only algebraic, but quadratic, and it is the number with the simplest continued fraction expansion (expressed with all ones) and nested radicals expansion (again, expressed with all ones).
Any nonnegative real number can be represented as a base
numeral using only the digits
0 and
1, and avoiding the digit sequence “
11”  this is called a
standard form, the representation thus obtained is unique. A base
numeral that includes the digit sequence “
11” can always be rewritten in
standard form, using the algebraic properties of the base
—most notably that
. For instance,
.
Despite using an
irrational number base, all
integers have a unique representation as a terminating (finite) base
expansion, but
only if in the
standard form. Nonintegers also have standard representations in base
, with
rational numbers having recurring representations. These representations are unique, except that numbers with a terminating expansion also have a nonterminating expansion, as they do in
base 10; for example,
0.99999….
Powers of ϕ in terms of ϕ and Fibonacci numbers
The following table expresses the powers of the
Golden ratio in terms of
itself and
Fibonacci numbers, where
is

Powers of


A005248 (n), n ≥ 0

6

5 + 8 ϕ

18

5

3 + 5 ϕ


4

2 + 3 ϕ

7

3

1 + 2 ϕ


2

1 + 1 ϕ

3

1

0 + 1 ϕ


0

1 + 0 ϕ

2

−1

( −1) + 1 ϕ


−2

2 + ( −1) ϕ

3

−3

( −3) + 2 ϕ


− 4

5 + ( −3) ϕ

7

− 5

( −8) + 5 ϕ


− 6

13 + ( −8) ϕ

18

A005248 Bisection of Lucas numbers: a (n) = L (2 n) = A000032 (2 n).

{2, 3, 7, 18, 47, 123, 322, 843, 2207, 5778, 15127, 39603, 103682, 271443, 710647, 1860498, 4870847, 12752043, 33385282, 87403803, 228826127, 599074578, 1568397607, ...}
Unique representation of integers as a sum of nonconsecutive powers of ϕ
Base 10

Sum of nonconsecutive powers of

Base

1

ϕ 0

1

2

ϕ 1 + ϕ −2

10.01

3

ϕ 2 + ϕ −2

100.01

4

ϕ 2 + ϕ 0 + ϕ −2

101.01

5

ϕ 3 + ϕ −1 + ϕ − 4

1000.1001

6

ϕ 3 + ϕ 1 + ϕ − 4

1010.0001

7

ϕ 4 + ϕ − 4

10000.0001

8

ϕ 4 + ϕ 0 + ϕ − 4

10001.0001

9

ϕ 4 + ϕ 1 + ϕ −2 + ϕ − 4

10010.0101

10

ϕ 4 + ϕ 2 + ϕ −2 + ϕ − 4

10100.0101

Phigital representation of some interesting numbers
 π = 100.0100101010010001010101000001010...ϕ (A102243)
 e = 100.0000100001001000000001000...ϕ (A105165)
See also
External links