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A260256
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Numbers n such that tau(n + 2) = tau(n - 2) where tau(k) = A000005(k).
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2
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5, 8, 9, 12, 15, 21, 24, 30, 36, 37, 39, 45, 53, 60, 67, 68, 69, 81, 84, 89, 93, 99, 105, 111, 112, 113, 117, 120, 121, 127, 129, 131, 143, 144, 157, 158, 165, 172, 173, 184, 185, 188, 195, 202, 203, 204, 207, 211, 215, 216, 217, 219, 222, 225, 226, 231, 248, 251, 276, 277, 279, 284, 288
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OFFSET
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1,1
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COMMENTS
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Pinner proves that this sequence is infinite, and in particular a(n) << n (log n)^7. The correct order is conjectured to be around n sqrt(log n). - Charles R Greathouse IV, Jul 21 2015
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LINKS
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FORMULA
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EXAMPLE
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8 is a member as 10 and 6 both have 4 divisors.
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MATHEMATICA
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Select[ Range@ 290, DivisorSigma[0, # - 2] == DivisorSigma[0, # + 2] &] (* Robert G. Wilson v, Jul 21 2015 *)
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PROG
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(Magma) [ n : n in [3..300] | Denominator((NumberOfDivisors(n-2))/(NumberOfDivisors(n+2))) eq 1 and Denominator((NumberOfDivisors(n+2))/(NumberOfDivisors(n-2))) eq 1];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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