|
%I #17 Feb 21 2017 03:37:04
%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
|
