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A103664
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Primes p such that the number of divisors of p-1 is less than the number of divisors of p+1.
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7
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2, 3, 5, 11, 17, 23, 29, 47, 53, 59, 71, 79, 83, 89, 107, 131, 139, 149, 167, 173, 179, 191, 197, 223, 227, 233, 239, 251, 263, 269, 293, 311, 317, 347, 359, 367, 383, 389, 419, 431, 439, 443, 449, 461, 467, 479, 499, 503, 509, 557, 563, 569, 587, 593, 599, 607
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(1)=2 because d(1)=1 < d(3)=2; a(2)=3 because d(2)=2 < d(4)=3.
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MAPLE
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with(numtheory): p:=proc(n) if isprime(n) and tau(n-1)<tau(n+1) then n else fi end: seq(p(n), n=1..1000); # Emeric Deutsch, Feb 22 2005
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MATHEMATICA
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Select[Prime[Range[1, 140]], Length[Divisors[ # - 1]] < Length[Divisors[ # + 1]] &]
Select[Prime[Range[200]], DivisorSigma[0, #-1]<DivisorSigma[0, #+1]&] (* Harvey P. Dale, May 31 2019 *)
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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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