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 A086006 Primes p such that 2*p-1 and 2*p+1 are semiprimes. 10
 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 December 8 15:17 EST 2023. Contains 367680 sequences. (Running on oeis4.)