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 A070552 Numbers n such that n and n+1 are semiprimes. 28
 9, 14, 21, 25, 33, 34, 38, 57, 85, 86, 93, 94, 118, 121, 122, 133, 141, 142, 145, 158, 177, 201, 202, 205, 213, 214, 217, 218, 253, 298, 301, 302, 326, 334, 361, 381, 393, 394, 445, 446, 453, 481, 501, 514, 526, 537, 542, 553, 565, 622, 633, 634, 694, 697 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A064911(a(n))*A064911(a(n)+1) = 1. - Reinhard Zumkeller, Dec 03 2009 LINKS D. W. Wilson, Table of n, a(n) for n = 1..10000 FORMULA a(n) >> n log n since either n or n+1 is in A100484. - Charles R Greathouse IV, Jul 21 2015 a(n) = A109373(n) - 1. - Zak Seidov Dec 19 2018 MATHEMATICA f[n_]:=Last/@FactorInteger[n]=={1, 1}||Last/@FactorInteger[n]=={2}; lst={}; Do[If[f[n]&&f[n+1], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Feb 25 2010 *) Flatten[Position[Partition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 700}], 2, 1], {1, 1}]] (* Harvey P. Dale, Feb 04 2015 *) Select[Range[700], PrimeOmega[#] == PrimeOmega[# + 1] == 2 &] (* Vincenzo Librandi, Jan 22 2016 *) PROG (PARI) forprime(p=3, 1e3, if(bigomega(2*p-1)==2, print1(2*p-1", ")); if(bigomega(2*p+1)==2, print1(2*p", "))) \\ Charles R Greathouse IV, Nov 09 2011 (PARI) is(n)=if(n%2, isprime((n+1)/2) && bigomega(n)==2, isprime(n/2) && bigomega(n+1)==2) \\ Charles R Greathouse IV, Sep 08 2015 (MAGMA) IsSemiprime:=func< n | &+[k[2]: k in Factorization(n)] eq 2 >; [ n: n in [4..700] | IsSemiprime(n) and IsSemiprime(n+1) ]; // Vincenzo Librandi, Jan 22 2016 CROSSREFS Cf. A001358, A007674, A039832, A100484. Sequence in context: A272527 A272308 A186778 * A272141 A289548 A001198 Adjacent sequences:  A070549 A070550 A070551 * A070553 A070554 A070555 KEYWORD nonn AUTHOR Sharon Sela (sharonsela(AT)hotmail.com), May 03 2002 EXTENSIONS More terms from Vladeta Jovovic, May 03 2002 STATUS approved

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Last modified August 3 12:02 EDT 2020. Contains 336198 sequences. (Running on oeis4.)