Palindrome Checker

What is a Palindrome?

A palindrome is a word, phrase, number, or sequence that reads the same forward and backward. The term comes from the Greek "palin" (again) and "dromos" (way, direction).

Types of Palindromes

Word Palindromes

Single words that read the same both ways: radar, level,civic, rotor, kayak.

Phrase Palindromes

Sentences that are palindromic when spaces and punctuation are ignored:

• "A man, a plan, a canal: Panama"
• "Was it a car or a cat I saw?"
• "Never odd or even"

Numeric Palindromes

Numbers like 121, 1331, 12321. Palindromic primes (like 131, 151, 181) are especially interesting mathematically.

Palindromes in Geocaching

Palindromes appear frequently in geocaching puzzles:

• Word puzzles: Find the palindrome hidden in clues
• Coordinate validation: Palindromic coordinate components
• Date puzzles: Palindrome dates (02/02/2020)
• Number sequences: Find or create palindromic numbers

Mathematical Properties

Interesting facts about palindromic numbers:

• All single-digit numbers are palindromes
• There are 9 two-digit palindromes (11, 22, ... 99)
• The 196 algorithm: repeatedly adding a number to its reverse sometimes creates palindromes, but 196 famously hasn't produced one after millions of iterations
• Palindromic primes: 2, 3, 5, 7, 11, 101, 131, 151, 181...

Finding Palindromes

To check if text is a palindrome:

1. Remove spaces and punctuation
2. Convert to same case (usually lowercase)
3. Compare with its reverse
4. If they match, it's a palindrome

Creating Palindromes

Methods to create palindromes:

• Mirroring: Append the reverse of the string
• Minimal append: Find shortest suffix to make it palindromic
• 196 algorithm: Add number to its reverse repeatedly