This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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