

A055153


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


12



4320, 4680, 26208, 20427264, 197064960, 21857648640, 57575890944, 88898072401645056, 301183421949935616, 9083288595228991885541376, 22290964134962716779872256, 230361837156847526055247872
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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 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(8), a(10), a(12) [and above] found by Michel Marcus, added by Gerard P. Michon, Jun 04 2009


STATUS

approved



