Simple palindromes
Find the number of 11 digit palindromes under the restriction that no digit may appear more than twice.
DETAILS AND ASSUMPTIONS
A palindrome is a sequence of characters that reads the same forwards and backwards. (Like 1234321)
The answer is 136080.
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1 solution
Since the number is a palindrome number, the first five digits will be same as the last five.....
Thus,
The first digit can have digits 1-9, thus having 9 possibilities, the second digit will have again 9 possibilities as this time zero has come into picture, similarly third, fourth, fifth and sixth digit will have 8, 7, 6 and 5 possibilities....
Therefore, total no. of permutations=
9 × 9 × 8 × 7 × 6 × 5
= 1 3 6 0 8 0