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A046315
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Odd semiprimes: odd numbers divisible by exactly 2 primes (counted with multiplicity).
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35
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9, 15, 21, 25, 33, 35, 39, 49, 51, 55, 57, 65, 69, 77, 85, 87, 91, 93, 95, 111, 115, 119, 121, 123, 129, 133, 141, 143, 145, 155, 159, 161, 169, 177, 183, 185, 187, 201, 203, 205, 209, 213, 215, 217, 219, 221, 235, 237, 247, 249, 253, 259, 265, 267, 287, 289
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The number of odd semiprimes < 10^n: 1, 19, 204, 1956, 18245, 168497, 1555811, 14426124, 134432669, ...; see A085770. - Robert G. Wilson v, Aug 25 2011.
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LINKS
| Zak Seidov, Table of n, a(n) for n = 1..1956
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MAPLE
| A046315 := proc(n) option remember; local r;
if n = 0 then RETURN(0) fi;
for r from A046315(n - 1) + 1 do
if r mod 2 = 1 and numtheory[bigomega](r) = 2
then RETURN(r) fi
od end:
seq(A046315(n), n=1..56); # - Peter Luschny, Feb 15 2011
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MATHEMATICA
| Reap[Do[If[Total[FactorInteger[n]][[2]] == 2, Sow[n]], {n, 1, 400, 2}]][[2, 1]] (* Zak Seidov *)
fQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; Select[2 Range@ 150 - 1, fQ] (* RGWv *)
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PROG
| (PARI) list(lim)=my(u=primes(primepi(lim\3)), v=List(), t); for(i=2, #u, for(j=i, #u, t=u[i]*u[j]; if(t>lim, break); listput(v, t))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 19 2011
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CROSSREFS
| Odd members of A001358.
Sequence in context: A046350 A175076 A046337 * A046372 A025045 A107987
Adjacent sequences: A046312 A046313 A046314 * A046316 A046317 A046318
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KEYWORD
| nonn
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Jun 15 1998.
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