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URL: https://oeis.org/A055153

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A055153

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

14

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

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OFFSET

1,1

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, Primitive Friendly Pairs with friends < 2^34 with denom < 20000

EXAMPLE

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

MATHEMATICA

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

PROG

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

CROSSREFS

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

Sequence in context: A165067 A236881 A190929 * A190011 A338537 A145312

Adjacent sequences: A055150 A055151 A055152 * A055154 A055155 A055156

KEYWORD

nonn

AUTHOR

Jud McCranie, Jun 16 2000

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

STATUS

approved