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A051676
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Composite numbers whose square has a prime number of divisors.
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3
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4, 8, 9, 25, 27, 32, 49, 64, 121, 125, 169, 243, 256, 289, 343, 361, 512, 529, 729, 841, 961, 1331, 1369, 1681, 1849, 2048, 2197, 2209, 2809, 3125, 3481, 3721, 4489, 4913, 5041, 5329, 6241, 6561, 6859, 6889, 7921, 9409, 10201, 10609, 11449, 11881, 12167
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OFFSET
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1,1
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COMMENTS
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LINKS
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MAPLE
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with(numtheory): A051676 := proc(n) option remember: local k: if(n=1)then return 4: fi: for k from procname(n-1)+1 do if(not isprime(k) and isprime(tau(k^2)))then return k: fi: od: end: seq(A051676(n), n=1..47); # Nathaniel Johnston, May 26 2011
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MATHEMATICA
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Select[Range[10^4], ! PrimeQ[ # ] && PrimeQ[DivisorSigma[0, #^2]] &]
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PROG
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(PARI) list(lim)=my(v=List(apply(p->p^2, primes(sqrtint(lim\=1)))), e); forprime(q=7, 2*logint(lim, 2)+1, e=q\2; forprime(p=2, sqrtnint(lim, e), listput(v, p^e))); Set(v) \\ Charles R Greathouse IV, Sep 18 2015
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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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