Palindromic Square 69696 = 2642
From "Keys to Infinity" by Clifford A. Pickover, Ed. Wiley 1995, page 159,160.
69696 is a remarkable palindrome.
Not only is it a palindromic square 2642 (see also WONplate 24),
not only has it exactly 10 palindromic prime factors 26 x 32 x 112,
it is also the largest ' smoothly undulating ' (of the form ababab...) square known to humanity.
Visit Sloane's database to find out the other smaller undulating squares at A016073.
I submitted a variant namely ' undulating primes ', watch out for entry A032758.
A less known fact (!?) is that 69696 is also the largest palindromic substring in 8117.
Thanks to G. L. Honaker, Jr. we know that 69696 is also the sum of a Twin Prime Pair.
69696 = 34847 + 34849
[ See Sloane's A037076 and Prime Curio! 69696 ].
Garland reports the following from "NUMBERS: Fun & Facts" by J. Newton Friend (1954) :
69696 is the product of two palindromes. Thus 69696 = 6336 x 11.
Note 6336 is unusual in that 6336 = 8 x (63 + 36) x 8 a nice palindromic expression.
[ October 24, 2005 ]
Another quality of 69696 is that when it is squared and then doubled
the outcome will be a pandigital number namely 9715064832 !
2 * 69696 ^ 2
Note again the palindromic expression itself !
(There exists another 5-digit palindrome with this property. Can you trace it ?)
Did you know that
69696 is the product of 192 * 363
and that 192 + 363 equals 555 which is a nice repdigit !
( Bonus : 363 192 = 171 yet another palindrome popping up ! )