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A179689
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Numbers with prime signature {7,2}, i.e., of form p^7*q^2 with p and q prime.
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7
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1152, 3200, 6272, 8748, 15488, 21632, 36992, 46208, 54675, 67712, 107163, 107648, 123008, 175232, 215168, 236672, 264627, 282752, 312500, 359552, 369603, 445568, 476288, 574592, 632043, 645248, 682112, 703125, 789507, 798848, 881792, 1013888
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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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MAPLE
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a:= proc(n) option remember; local k;
for k from 1+ `if` (n=1, 1, a(n-1))
while sort (map (x-> x[2], ifactors(k)[2]), `>`)<>[7, 2]
do od; k
end:
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MATHEMATICA
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f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 7}; Select[Range[10^6], f]
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PROG
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(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\4)^(1/7), t=p^7; forprime(q=2, sqrt(lim\t), if(p==q, next); listput(v, t*q^2))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 20 2011
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CROSSREFS
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Cf. A006881, A007304, A065036, A085986, A085987, A092759, A178739, A179642, A179643, A179644, A179645, A179646, A179664, A179665, A179666, A179667, A179668, A179669, A179670, A179671, A179672, A179688.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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