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A192991 Semiprimes times powers of 2. 2

%I

%S 8,12,16,18,20,24,28,30,32,36,40,42,44,48,50,52,56,60,64,66,68,70,72,

%T 76,78,80,84,88,92,96,98,100,102,104,110,112,114,116,120,124,128,130,

%U 132,136,138,140,144,148,152,154,156,160,164,168,170,172,174,176

%N Semiprimes times powers of 2.

%C Semiprimes times powers of 2 greater than 2^0 = 1.

%H Charles R Greathouse IV, <a href="/A192991/b192991.txt">Table of n, a(n) for n = 1..10000</a>

%F {A001358(i) * 2^j, j>0}.

%e 240 = 6th semiprime * 2^4 = 3 * 5 * 16.

%t upto=176;Select[Union[Flatten[2^Range[Ceiling[Log[2,upto]]] #&/@ Select[ Range[upto],PrimeOmega[#]==2&]]],#<=upto&](* _Harvey P. Dale_, Jul 19 2011 *)

%o (PARI) is(n)=my(e=valuation(n,2)); (e>2 && n>>e==1) || (e>1 && isprime(n>>e)) || (e>0 && bigomega(n>>e)==2) \\ _Charles R Greathouse IV_, Feb 21 2017

%Y Cf. A001358, A192990, A192992.

%K nonn,easy

%O 1,1

%A _Jonathan Vos Post_, Jul 13 2011

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Last modified October 23 11:35 EDT 2021. Contains 348211 sequences. (Running on oeis4.)