Palindromic Number

31,415,926,535,897,932,384,626,433,833,462,648,323,979,
853,562,951,413

Most readers likely know that palindromes are words, phrases, or sentences composed of the same letters reading forwards or backwards: "otto," "madam I'm Adam," "never odd or even".
Numbers obviously can also be palindromic: "11," "6116," "503305". Clearly one can invent palindromic numbers pretty much at will; still some are more interesting than others. The long number above is made from the first 27 digits of pi 'mirroring' themselves to create a palindrome. Nothing overly peculiar about that, but making it more interesting is the fact that it is also a prime number (of 53 digits). The next two such 'pi-palindromic' primes have 301 and 921 digits respectively. The study of prime numbers (evenly divisible only by themselves and 1) is virtually a book-length topic by itself. Prime numbers not only remain a central long-running and mysterious subject within mathematics (and specifically 'number theory'), but also play a key role in modern day encryption technology, and were central to Carl Sagan's best-selling novel/movie "Contact," as well.
BTW, the largest prime number yet known was recently discovered: 2^43,112,609 -1
(yes, it's even larger than the debt the current Administration will be leaving behind to the next President)