A plaindrome is a number whose hexadecimal digits are in nondecreasing order. The first few are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, ... (Sloane's A023757). The first few which are not plaindromes are 16, 32, 33, 48, 49, 50, 64, ..., corresponding to 
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Digit, Hexadecimal, Katadrome, Metadrome, Nialpdrome
Sloane, N. J. A. Sequences A023757 in "The On-Line Encyclopedia of Integer Sequences." http://www.research.att.com/~njas/sequences/.