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Fifty Five

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 ]

1 2  +  2 2  +  3 2  +  4 2  +  5 2  =  55

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
6 1  +  7 2  =  55
Note that 6712 equals 55 !

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

55 is the fourth Kaprekar number
55 2  =  3025  and  30  +  25  =  55  again !

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 )


A000081 Prime Curios! Prime Puzzle
Wikipedia 81 Le Nombre 81 Numberland 81














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