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A190106
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Numbers with prime factorization p^2*q^3*r^3 where p, q, and r are distinct primes.
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4
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5400, 9000, 10584, 13500, 24696, 26136, 36504, 37044, 49000, 62424, 68600, 77976, 95832, 114264, 121000, 143748, 158184, 165375, 169000, 171500, 181656, 207576, 231525, 237276, 266200, 289000, 295704, 332024, 353736, 361000, 363096
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OFFSET
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1,1
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LINKS
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FORMULA
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Sum_{n>=1} 1/a(n) = P(2)*P(3)^2/2 - P(2)*P(6)/2 - P(3)*P(5) + P(8) = 0.00085907862422456410530..., where P is the prime zeta function. - Amiram Eldar, Mar 07 2024
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MATHEMATICA
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f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 3, 3}; Select[Range[500000], f]
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PROG
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(PARI) list(lim)=my(v=List(), t1, t2); forprime(p=2, (lim\4)^(1/6), t1=p^3; forprime(q=p+1, (lim\t1)^(1/3), t2=t1*q^3; forprime(r=2, sqrt(lim\t2), if(p==r||q==r, next); listput(v, t2*r^2)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 20 2011
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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