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A004720 Delete all digits '1' from the sequence of nonnegative integers.

%I A004720 #63 Apr 20 2021 22:39:46
%S A004720 0,2,3,4,5,6,7,8,9,0,2,3,4,5,6,7,8,9,20,2,22,23,24,25,26,27,28,29,30,
%T A004720 3,32,33,34,35,36,37,38,39,40,4,42,43,44,45,46,47,48,49,50,5,52,53,54,
%U A004720 55,56,57,58,59,60,6,62,63,64,65,66,67,68,69,70,7,72,73,74,75
%N A004720 Delete all digits '1' from the sequence of nonnegative integers.
%C A004720 Similar to A004176. - _R. J. Mathar_, Oct 28 2008
%C A004720 More precisely, in A004176 the term becomes 0 if no digit remains, e.g., for 1 or 11, whereas here in such a case the integer is completely skipped (as in A004719, A004721, ... which are the analogs for deleting 0, 2, ...). - _M. F. Hasler_, Feb 01 2016
%H A004720 Sean A. Irvine, <a href="/A004720/b004720.txt">Table of n, a(n) for n = 1..1000</a>
%e A004720 The first nonnegative integer, 0, remains as a(1).
%e A004720 The second nonnegative integer, 1, completely disappears upon removal of the digit 1.
%e A004720 The third nonnegative integer, 2, remains as a(2).
%e A004720 The number 10 becomes a(10)=0.
%e A004720 The number 11 completely disappears upon removal of both its digits '1'.
%e A004720 The number 12 becomes a(11)=2.
%p A004720 f:= proc(n) local L,i;
%p A004720      L:= subs(1=NULL, convert(n,base,10));
%p A004720      if L = [] then NULL
%p A004720      else add(L[i]*10^(i-1),i=1..nops(L))
%p A004720      fi
%p A004720 end proc:
%p A004720 map(f, [$0..100]); # _Robert Israel_, Feb 07 2016
%t A004720 f[n_] := Block[{a = DeleteCases[ IntegerDigits[n], 1]}, If[a != {}, FromDigits@ a, b]]; DeleteCases[ Array[f, 75, 0], b] (* _Robert G. Wilson v_, Feb 05 2016 *)
%o A004720 (PARI) for(n=0,99,if(t=select(d->d!="1",Vec(Str(n))),print1(concat(t)","))) \\ _M. F. Hasler_, Feb 01 2016
%o A004720 (Python)
%o A004720 def A004720(n):
%o A004720     l = len(str(n-1))
%o A004720     m = (10**l-1)//9
%o A004720     k = n + l - 2 + int(n+l-1 >= m)
%o A004720     return 0 if k == m else int(str(k).replace('1','')) # _Chai Wah Wu_, Apr 20 2021
%Y A004720 See A004176 for another version.
%Y A004720 Cf. A004719, A004721, ...
%K A004720 base,nonn,nice,look
%O A004720 1,2
%A A004720 _N. J. A. Sloane_
%E A004720 Corrected by _T. D. Noe_, Sep 19 2008
%E A004720 Entry revised by _N. J. A. Sloane_ and _M. F. Hasler_ following a suggestion from _Sean A. Irvine_, Feb 01 2016