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A178905
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Numbers without 3 consecutive equal digits in any base b >= 2.
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2
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0, 1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 18, 19, 20, 22, 25, 36, 37, 38, 44, 45, 50, 51, 52, 74, 75, 76, 77, 89, 90, 100, 101, 102, 105, 109, 147, 150, 153, 154, 165, 166, 173, 178, 179, 180, 181, 204, 205, 210, 212, 214, 217, 293, 294, 299, 300, 301, 306, 308, 309, 329
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OFFSET
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1,3
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LINKS
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MATHEMATICA
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Prepend[Cases[Range[329], n_ /; NoneTrue[Range[2, (Sqrt[4 n - 3] - 1)/2], MatchQ[IntegerDigits[n, #], {___, d_, d_, d_, ___}] &]], 0] (* Vladimir Reshetnikov, Mar 20 2022 *)
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PROG
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(Python)
from sympy.ntheory.digits import digits
def three_in_a_row(s):
return any(s[i] == s[i+1] == s[i+2] for i in range(len(s) - 2))
def ok(n):
if n < 7: return True
b = 2
d = digits(n, b)[1:]
while len(d) >= 3:
if three_in_a_row(d): return False
b += 1
d = digits(n, b)[1:]
return True
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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