login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A055153 Numbers n such that sigma(n) = 7n/2. 12
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 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

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 30 06:11 EST 2020. Contains 338781 sequences. (Running on oeis4.)