[seqfan] Smallest digit makes the difference

[Eric Angelini]

Hello SeqFans,

Underline the smallest digit of any a(n) of the sequence U. 
Now a(n+1) is the smallest integer not occuring earlier that 
has two digits separated by the underlined digit.
Starting U with a(1)=1 should give:

U=1,10,11,12,21,23,13,32,20,22,24,31,34,14,43,25,35,30,33,36,41,45,15,
54,26,42,46,37,47,40,44,48,51,56,16,65,27,53,52,57,38,58,49,59,50,55,
61,67,17,76,28,64,62,68,39,63,69,60,66,71,78,18,87,29,75,72,79,70,77,
81,89,19,98,91,100,101,110,111,112,102,113,121,122,123,124,125,126,
127,128,129,132,134,143,145,154,156,165,167,176,178,187,189,198,201,
139,203,144,201,...

This is great fun to do by hand -- but
you know, typos, autocorrect, memory loss, etc.

Best,
É.