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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
OFFSET
1,1
COMMENTS
a(n) = A086005(n)/2.
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
Sequence in context: A024188 A196209 A196476 * A195685 A118587 A215164
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 07 2003
STATUS
approved