How to resolve the algorithm Sisyphus sequence step by step in the Ruby programming language

Published on 12 May 2024 09:40 PM

How to resolve the algorithm Sisyphus sequence step by step in the Ruby programming language

Table of Contents

Problem Statement

The Sisyphus sequence is an infinite sequence of positive integers that was devised in 2022 by Eric Angelini and Carole Dubois. The first term is 1. Subsequent terms are found by applying the following rule: 1 is odd and so the second term is: 1 + 2 = 3, because 2 is the smallest prime not yet added. 3 is odd and so the third term is: 3 + 3 = 6, because 3 is the smallest prime not yet added. 6 is even and so the fourth term is : 6 ÷ 2 = 3, and so on. Find and show on this page (in 10 lines of 10 terms), the first 100 terms of the sequence. What are the 1,000th, 10,000th, 100,000th and 1,000,000th terms of the sequence and, in each case, what is the highest prime needed to reach them? If it is difficult or impossible for your language or output device to meet all of these requirements, then just do what you reasonably can. What are the 10 millionth and 100 millionth terms and the highest prime needed to reach each one? By the time the 100 millionth term is reached, which number(s) under 250:

What is the number of the first term to equal 36? This was originally set as a challenge by Neil Sloane who was worried by its non-appearance and found by Russ Cox.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Sisyphus sequence step by step in the Ruby programming language

This Ruby code snippet generates prime numbers using the Prime library and then uses those prime numbers to create a sequence called "sisyphi" that follows a certain pattern. Here's how the code works:

  1. It first imports the Prime library, which provides methods for working with prime numbers.

  2. It defines a variable prime_gen that generates prime numbers using the Prime.each method. Initially, cur_prime is set to nil.

  3. It defines an enumerator called sisyphi using Enumerator.produce. This enumerator generates a sequence of numbers according to the following pattern:

    • If the current number is even, it divides it by 2.
    • If the current number is odd, it increments it by the next prime number (obtained from prime_gen) and stores that prime number in cur_prime.
  4. The code prints the first 100 numbers from the sisyphi sequence in groups of 10.

  5. It resets the prime_gen enumerator using rewind.

  6. It creates a hash called counter to count how often each number under 250 appears in the first 100,000,000 terms of the sisyphi sequence.

  7. It defines a variable idx which is initially set to 1000. This variable is used to print the element and corresponding prime number at certain intervals in the sequence.

  8. It defines a variable limit which is set to 100,000,000. This variable represents the limit up to which the code will generate terms in the sisyphi sequence.

  9. It uses the with_index method on the sisyphi enumerator to iterate over the sequence and count the occurrences of numbers under 250. It also prints the element and corresponding prime number at the intervals specified by idx.

  10. After generating the terms in the sisyphi sequence, it prints the numbers under 250 that do not appear in the first 100,000,000 terms.

  11. Finally, it finds and prints the numbers under 250 that appear most frequently in the first 100,000,000 terms.

This code essentially generates a sequence of numbers based on prime numbers and analyzes their distribution within a certain range.

Source code in the ruby programming language

require 'prime'

prime_gen = Prime.each
cur_prime = nil
sisyphi   = Enumerator.produce(1) {|n| n.even? ? n/2 : n += (cur_prime = prime_gen.next)}

sisyphi.first(100).each_slice(10){|s| puts "%4d"*s.size % s }

puts
prime_gen.rewind
counter = Hash.new(0)
count_until = 250
idx   = 1000
limit = 100_000_000   
sisyphi.with_index(1) do |n, i|
  counter[n] += 1 if n < count_until
  if i == idx then
    puts "element %11d is %11d, with prime %11d" % [i, n, cur_prime]
    break if idx >= limit
    idx *= 10
  end
end

puts "\nThese numbers under #{count_until} do not occur in the first #{limit} terms:"
puts ((1...count_until).to_a - counter.keys).join ", "

freq, nums = counter.group_by{|k, v| v}.max
puts "\nThese numbers under #{count_until} occur most frequent (#{freq} times) in the first #{limit} terms:"
puts nums.map(&:first).sort.join(", ")


  

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