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A049098
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Primes p such that p+1 is divisible by a square.
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8
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3, 7, 11, 17, 19, 23, 31, 43, 47, 53, 59, 67, 71, 79, 83, 89, 97, 103, 107, 127, 131, 139, 149, 151, 163, 167, 179, 191, 197, 199, 211, 223, 227, 233, 239, 241, 251, 263, 269, 271, 283, 293, 307, 311, 331, 337, 347, 349, 359, 367, 379, 383, 419, 431, 439, 443
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OFFSET
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1,1
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COMMENTS
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This sequence is infinite and its relative density in the sequence of primes is equal to 1 - Product_{p prime} (1-1/(p*(p-1)) = 1 - A005596 = 0.626044... (Mirsky, 1949). - Amiram Eldar, Feb 14 2021
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LINKS
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FORMULA
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EXAMPLE
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31 is a term because 32 is divisible by a square, 16.
101 is not a term because 102 = 2*3*17 is squarefree.
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MAPLE
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with(numtheory): a := proc (n) if isprime(n) = true and issqrfree(n+1) = false then n else end if end proc: seq(a(n), n = 1 .. 500); # Emeric Deutsch, Jun 21 2009
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MATHEMATICA
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Select[Prime[Range[200]], !SquareFreeQ[#+1]&] (* Harvey P. Dale, Mar 27 2011 *)
Select[Prime[Range[200]], MoebiusMu[# + 1] == 0 &] (* Alonso del Arte, Oct 18 2011 *)
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PROG
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(Haskell)
a049098 n = a049098_list !! (n-1)
a049098_list = filter ((== 0) . a008966 . (+ 1)) a000040_list
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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