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A154689
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Numbers n such that sigma_0(n-sigma_0(n))= sigma_0(n).
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2
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5, 7, 10, 13, 14, 18, 19, 26, 31, 38, 39, 43, 50, 55, 61, 62, 69, 72, 73, 78, 84, 86, 91, 95, 96, 98, 103, 108, 109, 110, 115, 119, 122, 123, 129, 133, 136, 138, 139, 145, 146, 151, 153, 159, 181, 182, 187, 190, 193, 199, 205, 206, 209, 213, 217, 218, 219, 221, 229
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OFFSET
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1,1
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COMMENTS
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If n is a term, then n - d(n) is in A175304. Indeed, if N = n - d(n), then d(N) = d(n). Now d(N+d(N)) = d(N+d(n)) = d(n) = d(N). - Vladimir Shevelev, Jul 29 2015
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LINKS
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MAPLE
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A000005 := proc(n) numtheory[tau](n) ; end: for n from 1 to 1000 do a05 := A000005(n) ; if A000005(n-a05) = a05 then printf("%d, ", n) ; fi; od: # R. J. Mathar, Jan 15 2009
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MATHEMATICA
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snQ[n_]:=Module[{nd=DivisorSigma[0, n]}, DivisorSigma[0, n-nd]==nd]; Select[ Range[300], snQ] (* Harvey P. Dale, Nov 10 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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