Phi’s Formula

May 15, 2012

The Phi Formula?

or … “Hey, it’s just an expression!”



It’s been noted by some who say they can “demystify phi” that phi is just one of an infinite series of numbers that can be constructed from the following expression using the square root (√) of integer numbers:

(1+√n) / 2

It just so happens that you get phi when you let n equal 5.  Let n be other integers and you get a series of numbers whose squares (see Phi2 in table in green) each exceed their root by a difference (see Δ in table in blue) that increases by 0.25 for each number in the series, as shown below.

Phi, being the 5th one in the series, just happens to be the one that produces a difference of 1 with its square, leading to the unique property that it shares with no other number:

Phi + 1 = Phi 2

1 n 2 Phi=(1+√n)/2 Phi2 Δ 1/Phi
1 1 2 1 1 0.00 1
1 2 2 1.207106781 1.457106781 0.25 0.828427125
1 3 2 1.366025404 1.866025404 0.50 0.732050808
1 4 2 1.5 2.25 0.75 0.666666667
1 5 2 1.618033989 2.618033989 1.00 0.618033989
1 6 2 1.724744871 2.974744871 1.25 0.579795897
1 7 2 1.822875656 3.322875656 1.50 0.548583770
1 8 2 1.914213562 3.664213562 1.75 0.522407750
1 9 2 2 4 2.00 0.5


So does this demystify phi, making it just one of a series of phi-like numbers?  Not necessarily, as this is only one aspect of phi’s unique properties.  Phi is also the only number that produces a difference of 1 with its reciprocal:

Phi – 1 = 1 / Phi

This is the key to its relationship to the golden section, which is based on sectioning a line in a way that fulfills two requirements:

A = B + C


A/B = B/C

A is to B as B is to C, where
A is 161.8% of B and B is 161.8% of C, and
B is 61.8% of A and C is 61.8% of B

Let n be any integer other than 5 and you won’t find the same pattern of consistent differences as shown above or the unique reciprocal and additive properties of phi.

Insights on phi’s formula in the table above contributed by Joseph Conklin.

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Leave a Comment

{ 3 comments… read them below or add one }

Kilogram April 2, 2013 at 1:56 pm

also if you take the squareroot(1+squareroot(1+squareroot(1+squareroot(1+squareroot(1+…))))) you get phi.


Ted December 4, 2013 at 11:03 pm

Phi is the second in an infinite sequence of n-nacci constants which all satisfy the equation;- F + 1/F^n =2

In the case of n=2 we get;-

Phi + 1/Phi^2 =2 ;(Where Phi = The Fibonacci constant)

When n=3 we get the Tribonacci constant
n=4 gives the Tetranacci constant
n=5 gives the Pentanacci constant
and so on ‘ad infinitum’… producing an infinite sequence of constants that converges on the value 2.

Phi is certainly unique in that it is the only n-nacci constant the produces a difference of 1 with its reciprocal, but it is still just the second in a well documented
sequence of n-nacci constants which of each have unique properties.



Daniel Baldock March 17, 2014 at 4:48 am



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