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A172509
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Numbers n such that Omega(n) = Omega(n - (digital sum of n)).
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1
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1, 10, 14, 15, 20, 27, 28, 30, 40, 50, 52, 60, 70, 75, 76, 78, 80, 90, 102, 105, 112, 124, 125, 132, 135, 136, 140, 164, 165, 176, 182, 186, 188, 204, 212, 224, 232, 234, 248, 252, 264, 273, 275, 279, 280, 290, 292, 306, 308, 315, 328, 336, 343
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OFFSET
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1,2
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COMMENTS
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Omega(n) is the number of prime divisors of n, A001222 (for n>0), taking Omega(0)=0.
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LINKS
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EXAMPLE
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a(1)=1 because Omega(1) = Omega(1 - (digital sum of 1)) = Omega(0) = 0;
a(2)=10 because Omega(10) = Omega(10 - (digital sum of 10)) = Omega(9) = 2.
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MAPLE
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filter:= proc(n) uses numtheory:
bigomega(n) = bigomega(n - convert(convert(n, base, 10), `+`))
end proc:
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MATHEMATICA
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Join[{1}, Select[Range[2, 400], PrimeOmega[#]==PrimeOmega[#-Total[ IntegerDigits[ #]]]&]] (* Harvey P. Dale, Jun 21 2021 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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