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A188061
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Numbers n such that (product of divisors of n) == 1 (mod sum of divisors of n).
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3
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4, 9, 16, 25, 49, 55, 64, 81, 121, 161, 169, 209, 256, 289, 351, 361, 529, 551, 625, 649, 729, 841, 961, 1024, 1079, 1189, 1369, 1407, 1443, 1681, 1849, 2015, 2209, 2289, 2401, 2809, 2849, 2915, 2975, 3401, 3481, 3721, 3857, 4096, 4489, 4599, 4887, 5041, 5329, 6049, 6241, 6319, 6561, 6889, 6993, 7921, 8569, 9409, 9701
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OFFSET
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1,1
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COMMENTS
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This sequence includes every number of the form p^(2n), where p is a prime. Other semiprime members include 55, 161, 209, 551, 649, 1079, 1189, 3401, 6049, 6319, 9701. Are there infinitely many nonsquare semiprimes in the sequence? Is there some simpler property of primes p and q that puts pq in this sequence?
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LINKS
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FORMULA
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MATHEMATICA
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mptQ[n_]:=Module[{dn=Divisors[n]}, Mod[Times@@dn, Total[dn]]==1]; Join[{1}, Select[Range[10000], mptQ]] (* Harvey P. Dale, Mar 28 2011 *)
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PROG
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(PARI) proddiv(n)=local(t); t=numdiv(n); if(t%2==0, n^(t\2), sqrtint(n)^t)
for(n=1, 10000, if(Mod(proddiv(n), sigma(n))==1, print1(n", ")))
(Python)
from gmpy2 import powmod, is_square, isqrt
from sympy import divisor_sigma
A188061_list = [n for n in range(1, 10**4) if powmod(isqrt(n) if is_square(n) else n, int(divisor_sigma(n, 0))//(1 if is_square(n) else 2), int(divisor_sigma(n, 1))) == 1] # Chai Wah Wu, Mar 10 2016
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CROSSREFS
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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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