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# Perrin Chalkboard

Welcome to the Perrin Chalkboard!  I will be presenting in this blog a series of chalkboards which discuss interesting properties of the Perrin sequence and related integer sequences. This blog starts as a simple discussion of the Perrin sequence (the original mention by Lucas in 1876 and Perrin in 1899). It is found that an immense amount of research on the associated elliptic curves has occurred over the last 115 years. The Perrin sequence ties together much of the mathematics discussed today as algebraic number theory and modular functions. It is also integral to the discussion of Fermat’s Last Theorem conjectured in 1637 but proved by Wiles in 1994.

Theorems will be presented without proofs. I think the subject matter will appeal to those interested in the properties of integer sequences, elliptic equations, and graph theory. Many sequences from OEIS (On-line Encyclopedia of Integer Sequences) will be discussed, uncovering hidden or less obvious properties.

The primary subject matter in this blog covers the properties of integer sequences. However, it is not until Chapter 17 that I cover the subject matter of the short paper published by Perrin in 1899.  This chapter then introduces the subject of integer partitions, followed by some geometric applications of the Perrin sequence and then turns to division algorithms derived from general properties of cubic equations and associated integer sequences.

I encourage any comments or suggestions to the chalkboard subjects.

Although the pdf files are freely provided, if you are interested or have questions regarding any chapter please feel free to contact me.

Richard Turk
March 2015

Updated July 2017

Click on the pdf to open the first chapter.. or  continue scrolling to find the latest Chapter and pdf!

Board1_generation

# Chapter 41- Convolution Recurrences from Inter Sequence Polynomials (CRISP)

The convolution of sequences using ISPs and their derivatives were described in a previous Chapter (see Chapter 36).  The Convolution Recurrences from Inter Sequence Polynomials (CRISP) program is designed to find the coefficients of second order and third order convolutions.  The  order of these sequences is found to be the sum of the orders or the component sequences.  By using the ISPS it was possible to find closed forms of the recurrence coefficients of the second and third derivatives of any linear second and third order parent recurrence.   This program (Mathematica) is shown in the attached pdf.

Convolution_Recurrences_CRISP

# Chapter 40-Discriminants and the Element Sequence Every linear integer sequence of a cubic polynomial has an associated element sequence.  The element sequence is the first derivative of the parent polynomial and easily obtained from its inter sequence polynomial.  Some sequences such as the Perrin sequence have an element sequence (the Padovan sequence) which is linearly proportional after rounding to its parent sequence.  This chapter discusses a method for finding this associated constant of proportion for any linear integer sequence based on the discriminant.  It is found that not all sequences exhibit this proportionality and an attempt is made to find condition for existence.

Discriminants and the Element Sequence

# Chapter 39A – An Algorithm for Higher Order Perrin Numbers Initiators are a set of numbers which can generate a sequence.  This appendix provides  simple cubic and quadratic polynomials for calculating the initiator sequences associated with 1st and higher order maximal independent sets.  Based on the constant g defined for the hypergeometric equation, sequence values can be readily calculated for odd values of g where g = 3 represents Perrin numbers.  The repeated pattern of a(n) = n for small odd n is common to these sequences and suggests a pattern in nature which leads to diversity and variation of structure.  An example of a DNA  sequence calculated from a higher order MIS sequence is shown (see above) to produce this variation in structure.

An Algorithm for Higher Order Perrin Numbers

# Chapter 39-Perrin Numbers, a Hypergeometric equation and Convolution Sequences

This chalkboard discusses the previously derived hypergeometric equation for calculating Perrin numbers.  The equation is also found to calculate the number of k-th order maximal independent sets in a cycle graph.  Convolution sequences are found to be related to the k-th order numbers and to two combinatorial numbers.

Perrin Numbers, a Hypergeometic Function and Convolution Sequences

# Chapter 38 – Solving Linear Differential Equations with Inter Sequence Polynomials This chalkboard demonstrates using ISPs to solve second, third and fourth order homogeneous ordinary differential equations.  These solutions agree with the Binet formula solution for second order and Binet-like formula for higher order ODEs. A comparison of these solutions to the Laplace Transform method is also shown.  Non-homogeneous ODEs are also found to be solvable by ISP sequences. Equations for finding the solutions to second, third and fourth order non-homogeneous ODEs by ISP are shown.

Solving_Linear_Differential_Equations_with_Intersequence_Polynomials

# Chapter 37- Higher Order Inter Sequence Polynomials

“You can’t go back and change the beginning, but you can start where you are and change the ending” – C. S. Lewis

This chapter concludes the topic of Inter sequence polynomials.  Many polynomial sequences can be defined by ISPs. Among these include Lucas-Fibonacci and Perrin-Padovan polynomial sequences. The derivative of the ISP is used as a solution to second order differential equations.

Higher Order InterSequencePolynomials

# Chapter 36- ISPs and Convolution A paradox is found between derivatives of the ISPs and discrete convolution of integer sequences. ISP derivatives are convolution operators!

InterSequencePolynomials_and_Convolution_