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

1,1

Comments

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

Links

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

Formula

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

Cf. A001358, A192990, A192992.

Sequence in context: A326111 A091375 A282671 * A083348 A174261 A063539

Adjacent sequences: A192988 A192989 A192990 * A192992 A192993 A192994

Keyword

nonn,easy

Author

Jonathan Vos Post, Jul 13 2011

Status

approved