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A055153 Numbers n such that sigma(n) = 7n/2. 9
4320, 4680, 26208, 20427264, 197064960, 21857648640, 57575890944, 88898072401645056, 301183421949935616, 9083288595228991885541376, 22290964134962716779872256, 230361837156847526055247872 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence also contains the term 230361837156847526055247872. - Yasutoshi Kohmoto, May 10 2008

301183421949935616 also belongs to this sequence. - Avinoam Kalma (a.kalma(AT)gmail.com), May 04 2009

22290964134962716779872256 is in this sequence. [From Gerard P. Michon, May 10 2009]

LINKS

G. P. Michon, Table of n, a(n) for n = 1..21

G. P. Michon, Multiperfect and hemiperfect numbers [From Gerard P. Michon, Jun 04 2009]

Walter Nissen, Abundancy : Some Resources

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.

MAPLE

with(numtheory); P:=proc(i) local n; for n from 1 by 1 to i do if sigma(n)/n=7/2 then; print(n); fi; od; end: P(100000000) # Paolo P. Lava, Sep 18 2008

MATHEMATICA

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

PROG

(PARI) is(n)=sigma(n, -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 A145312 A008409

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(8), a(10), a(12) [and above] found by Michel Marcus, added by Gerard P. Michon, Jun 04 2009

STATUS

approved

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Last modified June 25 20:26 EDT 2017. Contains 288730 sequences.