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 A309553 #20 Aug 07 2019 14:35:38 %S A309553 40,10880,715816960,3074457344902430720 %N A309553 Imperfect numbers of the form 2^(2^k-1)*F_1*F_2*...*F_(k-1), where F is a Fermat number. %C A309553 Numbers of this form are imperfect only for k = 2, 3, 4, 5. %H A309553 László Tóth, <a href="https://arxiv.org/abs/1111.4842">A survey of the alternating sum-of-divisors function</a>, arXiv:1111.4842 [math.NT], 2011-2014, end of section 8. %H A309553 László Tóth, <a href="https://doi.org/10.2478/ausm-2014-0007">A survey of the alternating sum-of-divisors function</a>, Acta Universitatis Sapientiae, Mathematica, Vol. 5, No. 1 (2013), pp. 93-107. %e A309553 For k=2, 2^3*F_1 = 8*5 = 40, so 40 is in the sequence. %Y A309553 Cf. A000215, A127724. %K A309553 nonn,fini,full %O A309553 1,1 %A A309553 _Jud McCranie_, Aug 07 2019