Find the smallest positive integer N such that a concatenation of N and 2*N is a pandigital number.

30729 has this feature, but it is not the smallest number.

(In reply to All of them by Charlie)

Given base 10, Charlie's N=13485 is the smallest. Yet, by definition a number is pandigital if its significant digits have each of the digits represented for its base. And in base 2, where N = 1, 2N = 10 and N||2N = 110 or, in base 10, 6 -- which is likely the smallest such number with bases unrestricted.

(Yes, I know, by default, if not stated, an inference is base 10 numbers -- yet, I wanted to be able to give an answer that was not computed by programmed code.) 

Posted by Dej Mar on 2015-12-19 19:30:21