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 A077374 #37 Jun 20 2025 10:45:46
%S A077374 1,3,5,7,9,11,15,21,315,1155,8925,32445,442365,815634435
%N A077374 Odd numbers m whose abundance by absolute value is at most 10, that is, -10 <= sigma(m) - 2m <= 10.
%C A077374 Apart from {1, 3, 5, 7, 9, 11, 15, 21, 315}, subset of A088012. Probably finite. - _Charles R Greathouse IV_, Mar 28 2011
%C A077374 a(15) > 10^13. - _Giovanni Resta_, Mar 29 2013
%C A077374 The abundance of the given terms a(1..14) is: (-1, -2, -4, -6, -5, -10, -6, -10, -6, -6, 6, 6, 6, -6). See also A171929, A188263 and A188597 for numbers with abundancy sigma(n)/n close to 2. - _M. F. Hasler_, Feb 21 2017
%C A077374 a(15) > 10^22. - _Wenjie Fang_, Jul 13 2017
%H A077374 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Abundance.html">Abundance</a>.
%e A077374 sigma(32445) = 64896 and 32445*2 = 64890, which makes the odd number 32445 six away from perfection: A(32445) = 6 and hence in this sequence.
%t A077374 Select[Range[1, 10^6, 2], -10 <= DivisorSigma[1, #] - 2 # <= 10 &] (* _Michael De Vlieger_, Feb 22 2017 *)
%o A077374 (PARI) forstep(n=1,442365,2,if(abs(sigma(n)-2*n)<=10,print1(n,",")))
%Y A077374 Contains odd terms of: A191363, A088831, A125246, A088832, A141548, A087167, A125247, A088833, A101223, A223609.
%Y A077374 Cf. A033879, A033880, A000203, A088012.
%K A077374 nonn,hard,more
%O A077374 1,2
%A A077374 _Jason Earls_, Nov 30 2002
%E A077374 a(14) from _Farideh Firoozbakht_, Jan 12 2004