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%I #9 Feb 01 2024 15:44:16
%S 0,1,2,3,4,5,6,7,8,9,10,11,20,21,22,30,31,32,33,40,41,42,43,44,50,51,
%T 52,53,54,55,60,61,62,63,64,65,66,70,71,72,73,74,75,76,77,80,81,82,83,
%U 84,85,86,87,88,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105
%N a(0)=0; for n>0, a(n) = smallest number that is not a concatenation of any number of distinct earlier terms in increasing order.
%C After 11 we can see 1,2 -> 12, 1,3 -> 13, etc., but not 20.
%H Michael S. Branicky, <a href="/A084383/b084383.txt">Table of n, a(n) for n = 0..10000</a>
%o (Python)
%o from itertools import islice
%o def incats(s, L):
%o if s == "": return True
%o return any(s.startswith(w) and incats(s[len(w):], L[i+1:]) for i, w in enumerate(L))
%o def agen(): # generator of terms
%o L, an, s = ["0"], 1, "1"
%o yield from [0]
%o while True:
%o yield an
%o L.append(s)
%o while incats((s:=str(an)), L):
%o an += 1
%o print(list(islice(agen(), 70))) # _Michael S. Branicky_, Feb 01 2024
%Y Hannah Rollman's numbers: A048991, A048992.
%K nonn,base
%O 0,3
%A _Amarnath Murthy_, May 29 2003
%E More terms from _Patrick De Geest_, Jun 03 2003
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