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A216793 Numbers n such that GCD(sigma(n), n) > GCD(sigma(m), m) for all m < n. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(30) > 10^9.

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

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.

PROG

(PARI) mgcdab(n) = { m = 0; for (i=1, n, g = gcd(sigma(i), i); if (g > m, m = g; print1(i, ", "); ); ); }

CROSSREFS

Cf. A009194.

Sequence in context: A263928 A219362 A226476 * A294900 A064510 A228383

Adjacent sequences:  A216790 A216791 A216792 * A216794 A216795 A216796

KEYWORD

nonn

AUTHOR

Michel Marcus, Sep 16 2012

EXTENSIONS

a(30)-a(32) from Donovan Johnson, Sep 17 2012

STATUS

approved

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Last modified July 23 11:44 EDT 2019. Contains 325254 sequences. (Running on oeis4.)