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%I #34 Feb 16 2024 10:12:19
%S 4320,4680,26208,20427264,197064960,21857648640,57575890944,
%T 88898072401645056,301183421949935616,9083288595228991885541376,
%U 22290964134962716779872256,230361837156847526055247872
%N Numbers n such that sigma(n) = 7n/2.
%C This sequence also contains the term 230361837156847526055247872. - _Yasutoshi Kohmoto_, May 10 2008
%C 301183421949935616 also belongs to this sequence. - Avinoam Kalma (a.kalma(AT)gmail.com), May 04 2009
%C 22290964134962716779872256 is in this sequence. [From _Gerard P. Michon_, May 10 2009]
%H G. P. Michon, <a href="/A055153/b055153.txt">Table of n, a(n) for n = 1..21</a>
%H G. P. Michon, <a href="http://www.numericana.com/answer/numbers.htm#multiperfect">Multiperfect and hemiperfect numbers</a> [From _Gerard P. Michon_, Jun 04 2009]
%H Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a>
%H Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a>
%H Walter Nissen, <a href="http://upforthecount.com/math/ffp8.html">Primitive Friendly Pairs with friends < 2^34 with denom < 20000</a>
%e Sigma(4320)=15120=7*4320/2, so 4320 is in the sequence.
%t Do[If[DivisorSigma[1, m]==3.5*m, Print[m]], {m, 2*10^8}]
%o (PARI) is(n)=sigma(n,-1)==7/2 \\ _Charles R Greathouse IV_, Mar 09 2014
%Y Cf. A007539, A000396, A005820, A027687, A000203, A141643, A141645.
%K nonn
%O 1,1
%A _Jud McCranie_, Jun 16 2000
%E Terms confirmed through a(5) by _Ray Chandler_, Sep 18 2008
%E a(6) and a(7) found by _Yasutoshi Kohmoto_ and confirmed by _Washington Bomfim_, Oct 19 2008
%E Edited by _N. J. A. Sloane_, Sep 19 2008, Apr 18 2009
%E a(8), a(10), a(12) [and above] found by Michel Marcus, added by _Gerard P. Michon_, Jun 04 2009
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