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A340835 a(n) is the least k such that the digit reversal of k is greater than or equal to n.

%I A340835 #36 Mar 14 2021 14:26:15
%S A340835 0,1,2,3,4,5,6,7,8,9,11,11,12,12,12,12,12,12,12,12,12,12,13,13,13,13,
%T A340835 13,13,13,13,13,13,14,14,14,14,14,14,14,14,14,14,15,15,15,15,15,15,15,
%U A340835 15,15,15,16,16,16,16,16,16,16,16,16,16,17,17,17,17,17,17
%N A340835 a(n) is the least k such that the digit reversal of k is greater than or equal to n.
%C A340835 A004086 gives the digit reversal of a number.
%C A340835 All positive terms belong to A070698.
%C A340835 This sequence is nondecreasing.
%H A340835 Rémy Sigrist, <a href="/A340835/b340835.txt">Table of n, a(n) for n = 0..10000</a>
%F A340835 a(n) <= n + 1 with equality iff n = 10^k for some k > 0.
%e A340835 For n = 1000:
%e A340835 - A004086(k) < 1000 for any k <= 1000,
%e A340835 - A004086(1001) = 1001 >= 1000,
%e A340835 - so a(1000) = 1001.
%o A340835 (PARI) { base = 10; k = 0; r = 0; for (n=0, 67, while (r<n, r = fromdigits(Vecrev(digits(k++, base)), base);); print1 (k ", ")) }
%o A340835 (Python)
%o A340835 def A340835(n):
%o A340835     if n == 0:
%o A340835         return 0
%o A340835     s = str(n)
%o A340835     for i, x in enumerate(s):
%o A340835         if x != '9':
%o A340835             break
%o A340835     else:
%o A340835         return n
%o A340835     s1, s2 = s[:i+1], s[i+1:]
%o A340835     if s2 == '':
%o A340835         if s1[-1] == '0':
%o A340835             return int(str(n+1)[::-1])
%o A340835         else:
%o A340835             return int(s[::-1])
%o A340835     if int(s2) <= 1:
%o A340835         return int('1'+s2[-2::-1]+s1[::-1])
%o A340835     else:
%o A340835         return int('1'+'0'*(len(s2)-1)+str(int(s1)+1)[::-1]) # _Chai Wah Wu_, Mar 14 2021
%Y A340835 Cf. A004086, A070698, A340836 (binary analog).
%K A340835 nonn,base
%O A340835 0,3
%A A340835 _Rémy Sigrist_, Mar 13 2021