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A282515
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Numbers m such that phi(sum of the divisors of m) = phi(sum of the distinct prime divisors of m) where phi is the Euler totient function.
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2
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3, 6, 10, 22, 34, 142, 178, 214, 382, 862, 1402, 2302, 5182, 9098, 15398, 17398, 21178, 23602, 279934, 289558, 296734, 368062, 900754, 944782, 1079374, 1563442, 1572862, 1990654, 2116342, 2505886, 2584882, 2691574, 2858698, 2883058, 3351214, 3909046
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OFFSET
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1,1
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COMMENTS
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For n > 1, we observe that a(n) is semiprime of the form a(n) = 2p with p = 3, 5, 11, 17, 71, 89, 107, 191, 431, 701, 1151, 2591, 4549, 7699, 8699, 10589, 11801, ... Except for the primes 3, 4549 and 7699 in the first 35 terms (from 6 until 3909046), the primes p are of the form 6k - 1.
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LINKS
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EXAMPLE
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MAPLE
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with(numtheory):
for n from 2 to 200000 do:
x:=divisors(n):n0:=nops(x):y:=factorset(n):n1:=nops(y):
s0:=sum(‘x[i]’, ‘i’=1..n0):s1:=sum(‘y[i]’, ‘i’=1..n1):
if phi(s1)=phi(s0)
then
print(n):
else
fi:
od:
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MATHEMATICA
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Select[Range[10^6], EulerPhi@ DivisorSigma[1, #] == EulerPhi[Total@ FactorInteger[#][[All, 1]]] &] (* Michael De Vlieger, Feb 17 2017 *)
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PROG
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(PARI) isok(n) = my(f=factor(n)); eulerphi(sigma(n)) == eulerphi(vecsum(f[, 1])); \\ Michel Marcus, Feb 25 2017
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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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