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A239802
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Numbers n such that if x = n - phi(n) then n = sigma(x) - x, where phi(n) is the Euler totient function.
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1
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36, 42, 186, 222, 270, 390, 396, 440, 656, 2220, 4140, 5622, 9400, 20214, 94816, 282540, 17578122, 85046840, 125948800, 145805120, 434435360
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OFFSET
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1,1
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COMMENTS
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Fixed points of the transform n -> sigma(n-phi(n)) - n + phi(n).
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LINKS
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EXAMPLE
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phi(222) = 72 and 222 - 72 = 150; sigma(150) = 372 and 372 - 150 = 222.
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MAPLE
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with(numtheory); P:=proc(q) local n; k:=0;
for n from 1 to q do if 2*n=sigma(n-phi(n))+phi(n) then print(n);
fi; od; end: P(10^9);
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PROG
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(PARI) isok(n) = (x = n - eulerphi(n)) && (n == sigma(x) - x); \\ Michel Marcus, Mar 28 2014
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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