A192991 Semiprimes times powers of 2.

8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 44, 48, 50, 52, 56, 60, 64, 66, 68, 70, 72, 76, 78, 80, 84, 88, 92, 96, 98, 100, 102, 104, 110, 112, 114, 116, 120, 124, 128, 130, 132, 136, 138, 140, 144, 148, 152, 154, 156, 160, 164, 168, 170, 172, 174, 176

Offset: 1

Author

Jonathan Vos Post, Jul 13 2011

Keywords

• nonn
• easy

Comments

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

Examples

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

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A192990, A192992.

Programs

Mathematica

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

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

Formula

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