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 A086006 Primes p such that 2*p-1 and 2*p+1 are semiprimes. 9
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) = A086005(n)/2. LINKS T. D. Noe, Table of n, a(n) for n=1..10000 FORMULA A064911(2*a(n)-1) * A064911(2*a(n)+1) = 1. - Reinhard Zumkeller, Aug 08 2013 EXAMPLE 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. MATHEMATICA Select[Prime[Range[400]], PrimeOmega[2#-1]==PrimeOmega[2#+1]==2&] (* Harvey P. Dale, Jun 23 2016 *) PROG (PARI) isok(n) = isprime(n) && (bigomega(2*n+1) == 2) && (bigomega(2*n-1) == 2) \\ Michel Marcus, Aug 01 2013 (Haskell) a086006 = flip div 2 . a086005  -- Reinhard Zumkeller, Aug 08 2013 CROSSREFS Cf. A001358, A000040. Sequence in context: A024188 A196209 A196476 * A195685 A118587 A215164 Adjacent sequences:  A086003 A086004 A086005 * A086007 A086008 A086009 KEYWORD nonn AUTHOR Reinhard Zumkeller, Jul 07 2003 STATUS approved

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Last modified August 25 16:17 EDT 2019. Contains 326324 sequences. (Running on oeis4.)