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 A223610 #31 Jul 09 2025 04:36:14 %S A223610 208,6976,8415,31815,351351,2077696,20487159,159030135,536559616, %T A223610 2586415095,137433972736,2199003332608,2305842988812599296 %N A223610 Numbers k whose abundance is 18: sigma(k) - 2*k = 18. %C A223610 Any term x of this sequence can be combined with any term y of A223608 to satisfy the property (sigma(x)+sigma(y))/(x+y) = 2, which is a necessary (but not sufficient) condition for two numbers to be amicable. - _Timothy L. Tiffin_, Sep 13 2016 %C A223610 Every number of the form 2^(j-1)*(2^j - 19), where 2^j - 19 is prime, is a term (cf. A096819). - _Jon E. Schoenfield_, Jun 02 2019 %e A223610 For k = 159030135, sigma(k) - 2*k = 18. %t A223610 Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == 18 &] (* _Vincenzo Librandi_, Sep 14 2016 *) %o A223610 (PARI) for(n=1, 10^8, if(sigma(n)-2*n==18, print1(n ", "))) %o A223610 (Magma) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq 18]; // _Vincenzo Librandi_, Sep 14 2016 %Y A223610 Cf. A000203, A033880, A096819, A223608 (deficiency 18). %K A223610 nonn,more %O A223610 1,1 %A A223610 _Donovan Johnson_, Mar 23 2013, at suggestion of _N. J. A. Sloane_ and _Robert G. Wilson v_ %E A223610 a(12) from _Giovanni Resta_, Mar 29 2013 %E A223610 a(13) from _Jon E. Schoenfield_ confirmed and added by _Max Alekseyev_, Jun 03 2025