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A216793
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Numbers n such that gcd(sigma(n), n) > gcd(sigma(m), m) for all m < n.
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3
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1, 6, 24, 28, 120, 496, 672, 4320, 4680, 8128, 26208, 30240, 32760, 174592, 199584, 293760, 435708, 523776, 2142720, 2178540, 8910720, 17428320, 20427264, 23569920, 33550336, 45532800, 91963648, 142990848, 459818240, 1379454720, 1476304896, 6039429120
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OFFSET
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1,2
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COMMENTS
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a(30) > 10^9.
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LINKS
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EXAMPLE
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a(2) = 6 because gcd(sigma(1), 1) = 1, gcd(sigma(2), 2) = 1, gcd(sigma(3), 3) = 1, gcd(sigma(4), 4) = 1, gcd(sigma(5), 5) = 1, and for n = 6, we have gcd(sigma(6), 6) = 6, which is greater than the five preceding.
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PROG
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(PARI) mgcdab(n) = { m = 0; for (i=1, n, g = gcd(sigma(i), i); if (g > m, m = g; print1(i, ", "); ); ); }
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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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