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A355221 The k-th leftmost digit of a(n) is the least of the k leftmost digits of n.

%I A355221 #18 Jun 30 2023 15:49:57
%S A355221 0,1,2,3,4,5,6,7,8,9,10,11,11,11,11,11,11,11,11,11,20,21,22,22,22,22,
%T A355221 22,22,22,22,30,31,32,33,33,33,33,33,33,33,40,41,42,43,44,44,44,44,44,
%U A355221 44,50,51,52,53,54,55,55,55,55,55,60,61,62,63,64,65,66,66
%N A355221 The k-th leftmost digit of a(n) is the least of the k leftmost digits of n.
%C A355221 Leading zeros are ignored.
%H A355221 Rémy Sigrist, <a href="/A355221/b355221.txt">Table of n, a(n) for n = 0..10000</a>
%F A355221 a(n) <= n with equality iff n belongs to A009996.
%F A355221 a(a(n)) = a(n).
%e A355221 For n = 1402: min({1}) = 1, min({1, 4}) = 1, min({1, 4, 0}) = 0, min({1, 4, 0, 2}) = 0, so a(1402) = 1100.
%t A355221 Table[FromDigits[Table[Min[Take[IntegerDigits[n],d]],{d,IntegerLength[n]}]],{n,0,70}] (* _Harvey P. Dale_, Jun 30 2023 *)
%o A355221 (PARI) a(n, base=10) = { my (d=digits(n, base), m=oo); for (k=1, #d, d[k]=m=min(m, d[k])); fromdigits(d, base) }
%o A355221 (Python)
%o A355221 def a(n):
%o A355221     s, m = str(n), "9"
%o A355221     return int("".join((m:=min(m, s[k])) for k in range(len(s))))
%o A355221 print([a(n) for n in range(68)]) # _Michael S. Branicky_, Jun 24 2022
%o A355221 (Python)
%o A355221 from itertools import accumulate
%o A355221 def A355221(n): return int(''.join(accumulate(str(n),func=min))) # _Chai Wah Wu_, Jun 25 2022
%Y A355221 See A355222, A355223  and A355224 for similar sequences.
%Y A355221 Cf. A009996 (fixed points), A342126 (binary analog).
%K A355221 nonn,base,easy
%O A355221 0,3
%A A355221 _Rémy Sigrist_, Jun 24 2022