OFFSET
1,2
COMMENTS
Numbers n that do not occur in the concatenation of 1,2,3...,n-1.
Every power of 10 is a member, which proves that the sequence is infinite. - N. J. A. Sloane, Jul 23 2007
The asymptotic density of the sequence is zero. The number of k-digit terms is A132133 = (9, 45, 270, 2104, ...), k = 1, 2, .... These are the first difference of the indices of powers of 10, T = (1, 10, 55, 325, 2429, ...), which we get as partial sums if we prefix A132133(0) = 1 corresponding to the number 0. - M. F. Hasler, Oct 24 2019
LINKS
M. F. Hasler, Table of n, a(n) for n = 1..2428
EXAMPLE
The first number not in this sequence is the early bird "12" which occurs as concatenation of 1 and 2.
PROG
(PHP) $s="0"; for(; ++$i < 2000; $s .= $i) if( !strpos($s, "$i")) echo $i, ", ";
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Jul 23 2007
STATUS
approved