This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A055153 #40 Jun 07 2025 08:13:54
%S A055153 4320,4680,26208,20427264,197064960,21857648640,57575890944,
%T A055153 88898072401645056,301183421949935616,9083288595228991885541376,
%U A055153 22290964134962716779872256,230361837156847526055247872
%N A055153 Numbers k such that sigma(k) = 7k/2.
%H A055153 G. P. Michon, <a href="/A055153/b055153.txt">Table of n, a(n) for n = 1..21</a>
%H A055153 G. P. Michon, <a href="http://www.numericana.com/answer/numbers.htm#multiperfect">Multiperfect and hemiperfect numbers</a>
%H A055153 Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a>
%H A055153 Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a>
%H A055153 Walter Nissen, <a href="http://upforthecount.com/math/ffp8.html">Primitive Friendly Pairs with friends < 2^34 with denom < 20000</a>
%e A055153 Sigma(4320)=15120=7*4320/2, so 4320 is in the sequence.
%t A055153 Do[If[DivisorSigma[1, m]==3.5*m, Print[m]], {m, 2*10^8}]
%o A055153 (PARI) is(k)=sigma(k,-1)==7/2 \\ _Charles R Greathouse IV_, Mar 09 2014
%Y A055153 Cf. A007539, A000396, A005820, A027687, A000203, A141643, A141645.
%K A055153 nonn
%O A055153 1,1
%A A055153 _Jud McCranie_, Jun 16 2000
%E A055153 Terms confirmed through a(5) by _Ray Chandler_, Sep 18 2008
%E A055153 a(6) and a(7) found by _Yasutoshi Kohmoto_ and confirmed by _Washington Bomfim_, Oct 19 2008
%E A055153 Edited by _N. J. A. Sloane_, Sep 19 2008, Apr 18 2009
%E A055153 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