The palindrome Fifty Five or 55

55 is the sum of the following five consecutive square numbers ( 1 + 4 + 9 + 16 + 25 )
thus making it the fifth square pyramidal number [ formula : n(n+1)(2n+1)/6 ]

55 as a Cubic Invariant
5³ + 5³ = 250
2³ + 5³ + 0³ = 133
1³ + 3³ + 3³ = 55

55 is the tenth Fibonacci number
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

55 is the fourth palindromic triangular number
1, 3, 6, 55, 66, 171, ...

55 is the sum of the first ten numbers
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10

55 is expressible as the sum of five consecutive integers
9 + 10 + 11 + 12 + 13

55 is the sum of two consecutive numbers and powers

Note that 67 – 12 equals 55 !

55 is expressible as the sum of two consecutive integers
27 + 28

55 is the fourth Kaprekar number

55 can be multiplied with 10 consecutive odd numbers
from 91 to 109 and all the products will be palindromic !
Palindromes 5005 up to 5995.
( From Clifford A. Pickover, “Wonders of Numbers”, Chapter 57, p. 141 )