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A086006
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Primes p such that 2*p-1 and 2*p+1 are semiprimes.
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10
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17, 43, 47, 61, 71, 101, 107, 109, 151, 197, 223, 317, 349, 421, 461, 521, 569, 631, 673, 701, 821, 881, 919, 947, 971, 991, 1051, 1091, 1109, 1153, 1181, 1217, 1231, 1259, 1321, 1361, 1367, 1549, 1693, 1801, 1847, 1933, 1951, 1979, 2143, 2207
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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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FORMULA
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EXAMPLE
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101 is prime and 2*101-1=201=3*67, 2*101+1=203=7*29, therefore 101 is a term.
It is the sixth term and a(6)=101=A086005(6)/2.
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MATHEMATICA
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Select[Prime[Range[400]], PrimeOmega[2#-1]==PrimeOmega[2#+1]==2&] (* Harvey P. Dale, Jun 23 2016 *)
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PROG
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(PARI) isok(n) = isprime(n) && (bigomega(2*n+1) == 2) && (bigomega(2*n-1) == 2) \\ Michel Marcus, Aug 01 2013
(Haskell)
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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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