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A192991 Semiprimes times powers of 2. 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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 26 05:10 EST 2020. Contains 331273 sequences. (Running on oeis4.)