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A004722
Delete all digits 3 from the terms of the sequence of nonnegative integers.
10
0, 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1, 14, 15, 16, 17, 18, 19, 20, 21, 22, 2, 24, 25, 26, 27, 28, 29, 0, 1, 2, 4, 5, 6, 7, 8, 9, 40, 41, 42, 4, 44, 45, 46, 47, 48, 49, 50, 51, 52, 5, 54, 55, 56, 57, 58, 59, 60, 61, 62, 6, 64, 65, 66, 67, 68, 69, 70, 71, 72, 7, 74, 75, 76
OFFSET
0,3
COMMENTS
Very similar to A004178, except that 3-repdigits (A002277) are completely removed from the sequence, whereas A004178 has 0's in their place. It is thus guaranteed that a(n) = n only when n < 3. - Alonso del Arte, Oct 18 2012
LINKS
FORMULA
a(n) = n for -1 < n < 3;
a(n) = A004178(n + 1) for 2 < n < 32,
a(n) = A004178(n + 2) for 31 < n < 331,
a(n) = A004178(n + 3) for 330 < n < 3330,
a(n) = A004178(n + 4) for 3329 < n < 33329, etc. - Alonso del Arte, Oct 21 2012
MATHEMATICA
endAt = 103; Delete[Table[FromDigits[DeleteCases[IntegerDigits[n], 3]], {n, 0, endAt}], Table[{(10^expo - 1)/3 + 1}, {expo, Floor[Log[10, endAt]]}]] (* Alonso del Arte, Apr 29 2019 *)
PROG
(MATLAB) m=1;
for u=0:1000
v=dec2base(u, 10)-'0'; v = v(v~=3);
if length(v)>0; sol(m)=(str2num(strrep(num2str(v), ' ', ''))); m=m+1; end;
end
sol % Marius A. Burtea, May 07 2019
(Python)
def A004722(n):
l = len(str(n))
m = (10**l-1)//3
k = n + l - int(n+l < m)
return 2 if k == m else int(str(k).replace('3', '')) # Chai Wah Wu, Apr 20 2021
KEYWORD
base,nonn
EXTENSIONS
Sean A. Irvine pointed out erroneous terms in b-file and confirmed correction, Apr 28 2019
Name edited by Felix Fröhlich, Apr 29 2019
STATUS
approved