A055153 Numbers k such that sigma(k) = 7k/2.

4320, 4680, 26208, 20427264, 197064960, 21857648640, 57575890944, 88898072401645056, 301183421949935616, 9083288595228991885541376, 22290964134962716779872256, 230361837156847526055247872

Offset: 1

Author

Jud McCranie, Jun 16 2000

Keywords

• nonn

Examples

			Sigma(4320)=15120=7*4320/2, so 4320 is in the sequence.
		

Links

• G. P. Michon, Table of n, a(n) for n = 1..21
• G. P. Michon, Multiperfect and hemiperfect numbers
• Walter Nissen, Abundancy : Some Resources
• Walter Nissen, Abundancy : Some Resources
• Walter Nissen, Primitive Friendly Pairs with friends < 2^34 with denom < 20000

Crossrefs

Cf. A007539, A000396, A005820, A027687, A000203, A141643, A141645.

Programs

Mathematica

Do[If[DivisorSigma[1, m]==3.5*m, Print[m]], {m, 2*10^8}]

PARI

is(k)=sigma(k,-1)==7/2 \\ Charles R Greathouse IV, Mar 09 2014

Extensions

Terms confirmed through a(5) by Ray Chandler, Sep 18 2008

a(6) and a(7) found by Yasutoshi Kohmoto and confirmed by Washington Bomfim, Oct 19 2008

Edited by N. J. A. Sloane, Sep 19 2008, Apr 18 2009

a(9) from Avinoam Kalma, a(12) from Yasutoshi Kohmoto, and a(8), a(10), a(13)-a(21) from Michel Marcus, added by Gerard P. Michon, Jun 04 2009