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

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, 3, 32, 33, 34, 35, 36, 37, 38, 39, 40, 4, 42, 43, 44, 45, 46, 47, 48, 49, 50, 5, 52, 53, 54, 55, 56, 57, 58, 59, 60, 6, 62, 63, 64, 65, 66, 67, 68, 69, 70, 7, 72, 73, 74, 75

Offset: 1

Author

N. J. A. Sloane

Keywords

• base
• nonn
• nice
• look

Comments

Similar to A004176. - R. J. Mathar, Oct 28 2008

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

Examples

			The first nonnegative integer, 0, remains as a(1).
The second nonnegative integer, 1, completely disappears upon removal of the digit 1.
The third nonnegative integer, 2, remains as a(2).
The number 10 becomes a(10)=0.
The number 11 completely disappears upon removal of both its digits '1'.
The number 12 becomes a(11)=2.
		

Links

• Sean A. Irvine, Table of n, a(n) for n = 1..1000

Crossrefs

See A004176 for another version.

Cf. A004719, A004721, ...

Programs

Maple

f:= proc(n) local L,i;
     L:= subs(1=NULL, convert(n,base,10));
     if L = [] then NULL
     else add(L[i]*10^(i-1),i=1..nops(L))
     fi
end proc:
map(f, [$0..100]); # Robert Israel, Feb 07 2016

Mathematica

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 *)

PARI

for(n=0,99,if(t=select(d->d!="1",Vec(Str(n))),print1(concat(t)","))) \\ M. F. Hasler, Feb 01 2016

Python

def A004720(n):
    l = len(str(n-1))
    m = (10**l-1)//9
    k = n + l - 2 + int(n+l-1 >= m)
    return 0 if k == m else int(str(k).replace('1','')) # Chai Wah Wu, Apr 20 2021

Extensions

Corrected by T. D. Noe, Sep 19 2008

Entry revised by N. J. A. Sloane and M. F. Hasler following a suggestion from Sean A. Irvine, Feb 01 2016