Enigma 1697: Binary palindrome
From New Scientist #2864, 12th May 2012 [link]
I have before me a number, which when written in binary is palindromic and has n digits. If I told you the value of n, and you wrote a list of all the possible palindromic binary numbers of length n, your list would have n numbers in it.
If your list was in ascending numeric order, and I told you the difference between my number and the next higher number in the list, you would be able to identify my number.
What is my number, in decimal form?