A004721 Delete all 2's from the sequence of nonnegative integers.

0, 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1, 13, 14, 15, 16, 17, 18, 19, 0, 1, 3, 4, 5, 6, 7, 8, 9, 30, 31, 3, 33, 34, 35, 36, 37, 38, 39, 40, 41, 4, 43, 44, 45, 46, 47, 48, 49, 50, 51, 5, 53, 54, 55, 56, 57, 58, 59, 60, 61, 6, 63, 64, 65, 66, 67, 68, 69, 70, 71, 7, 73, 74, 75

Offset: 0

Author

N. J. A. Sloane

Keywords

• base
• nonn

Crossrefs

Cf. A004719, A004720, A004722, A004723, A004724, A004725, A004726, A004727, A004728.

Programs

Mathematica

d[n_]:=IntegerDigits[n]; t={0}; Do[If[Union[d[n]]!={2},n=FromDigits[DeleteCases[d[n],2]]; AppendTo[t,n]],{n,75}]; t (* Jayanta Basu, May 17 2013 *)

Python

def A004721(n):
    l = len(str(n))
    m = 2*(10**l-1)//9
    k = n + l - int(n+l < m)
    return 1 if k == m else int(str(k).replace('2','')) # Chai Wah Wu, Apr 20 2021