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A189990
Numbers with prime factorization p^2*q^6.
9
576, 1600, 2916, 3136, 7744, 10816, 18225, 18496, 23104, 33856, 35721, 53824, 61504, 62500, 87616, 88209, 107584, 118336, 123201, 140625, 141376, 179776, 210681, 222784, 238144, 263169, 287296, 322624, 341056, 385641, 399424, 440896, 470596
OFFSET
1,1
FORMULA
Sum_{n>=1} 1/a(n) = P(2)*P(6) - P(8) = A085548 * A085966 - A085968 = 0.003658..., where P is the prime zeta function. - Amiram Eldar, Jul 06 2020
MATHEMATICA
f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 6}; Select[Range[800000], f]
PROG
(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\4)^(1/6), t=p^6; forprime(q=2, sqrt(lim\t), if(p==q, next); listput(v, t*q^2))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 24 2011
CROSSREFS
Subsequence of A137484.
Sequence in context: A268773 A250789 A137484 * A064254 A281242 A067225
KEYWORD
nonn
AUTHOR
STATUS
approved