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

0,3

Links

Table of n, a(n) for n=0..73.

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 *)

Prog

(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

Crossrefs

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

Sequence in context: A154781 A118716 A004177 * A333838 A030544 A141213

Adjacent sequences: A004718 A004719 A004720 * A004722 A004723 A004724

Keyword

base,nonn

Author

N. J. A. Sloane

Status

approved