Number Five (5) and Phi

The number 5 is intrinsically related to Phi and the Fibonacci series.

Phi can be derived from several formulas based on the number 5.  The most traditional, based on the geometric construction of phi is this:

Phi, the golden ratio, as a function of root 5 + 1 / 2

This formula for phi can also be expressed all in fives as:

Φ = 5 ^ .5 * .5 + .5


Another formula for phi based entirely on 5’s, an original insight contributed by Erol Karazincir ([email protected]), is as follows:

Phi, the golden ratio, as a function of root ((5+root 5)/5-root 5))

And, as pointed out by W. Nathan Saunders, the terms in above representation of phi can be expressed in yet another way that involves four 5’s:

(5 + √5) x (5 – √5) = 5 + 5 + 5 + 5


Phi appears in the geometry of the 5-sided pentagon

Take a pentagon with 5 equal sides and connect all the points to form a 5-pointed star.  The ratios of the lengths of the resulting line segments are all based on phi.

phi, the golden proportion, in a pentagon

Phi appears in the natural logs and trigonmetric functions

Phi can be related to e, the base of natural logs,
through the inverse hyperbolic sine function:

Phi = e ^ asinh(.5)

Determining the nth number of the Fibonacci series

You can compute the nth number in the Fibonacci series (fn) using phi and root 5:

fn =  Phi n / 5½

 5 is the 5th Fibonacci number

5 is also the 5th of the Fibonacci numbers, including 0, 1, 2, 3, and 5.

5 appears in the human body, which has proportions based on phi

Another interesting aspect of phi and five is in relation to the design of the human body, which in addition to being based on phi relationships in its proportions, has:

  • 5 appendages from the torso, in the two arms, two legs and a head,
  • 5 appendages on each of legs and arms in the five fingers and five toes,
  • 5 openings on the face, and
  • 5 senses in sight, sound, touch, taste and smell.

5 deserves a “high 5” for its role in phi, don’t you think!

High fives for 5!


  1. Sergio Viana says

    Remember the 24 pattern?
    its a 12-12 right?
    5 appears again in a DODECAHEDRON, where this 12-sided polyhedron has each face being a pentagon :)

  2. RichMJones says

    In a spreadsheet enter a column where the following formula is repeated (1+1/previous value)

    Equations a column, e.., =1, =1+1/A1, =1+1/A2, …, =1+1/An

    This will generate successive values converging in Phi, also note the Phi’s generated with by starting with any initial value (not 1). – Amazing.

    In a spreadsheet enter a column where the following formula is repeated ( =Previous + Previous to that)

    Fib Equation:=0, =1, =A2+A3, =A3+A4, =A4+A5, …, =A(n)+A(n-1)

    (A1, A2 are inital values, enter other “seed” numbers (plus or minus) an see the results. Amazing.

    In adjacent columns, calculate ratios

    Equations For Smaller/Larger: =A3/A4, =A4/A5, =A5/A6, …, =A(n-1)/A(n)

    Equations For Larger/Smaller: =A4/A3, =A5/A4, =A6/A5, …, =A(n)/A(n-1)

    Ok so what is amazing?

    These equations and relationships are just the sort that would find application in nature.

    The interactive “one over plus one over” iteration represents the simplest version of the inverse proportion ratios (1/x) found in natural processed (forces?) and converging on natural replicated occurrence.

    The ratio of Fibonacci numbers is also well represented in nature, but it is not the high nth iteration of these that have relevance, it is the fact that they occur everywhere there is life and replicated and differentiated in evolution.

  3. Rhuben says

    Every fifth Fibonacci Sequence number is divisible by 5 also;
    10th : 55 = 5 x 11
    15th : 610 = 5 x 122
    20th : 6765 = 5 x 1353
    (P.S this also re-creates a new 24 digital root pattern in both the 5th Fib numbers sequence and the amounts that is divisible into it.)

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