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 A049030 #23 Feb 16 2020 03:19:46 %S A049030 16,3034,320243,32226805,3224444759,322465138002,32246681892518, %T A049030 3224670122682648,322467031114802292,32246703322412473945, %U A049030 3224670334023621455211,322467033422357645316809,32246703342390510922780778,3224670334240928188556405242 %N A049030 Sum of sigma(j) for 1<=j<10^n, where sigma(j) = A048050(j) is the sum of the proper divisors >1 of j (excluding 1 and n). %H A049030 Amiram Eldar, <a href="/A049030/b049030.txt">Table of n, a(n) for n = 1..36</a> (calculated from the b-file at A049000) %H A049030 Carlos Rivera, <a href="http://www.primepuzzles.net/problems/prob_023.htm">Problem 23.- Divisors (V) Aliquot sequences, Sociable Numbers</a>, Prime Puzzles and Problems Connection. %F A049030 At a(3) = 320243, for example, take a(3) from A049000: 820741 - 500498 = 320243. Compute 500498 from 999*1000/2 = 499500, split evenly and reverse to 500499 - 1 = 500498. Add a 9 and 0 for each successive term. %F A049030 a(n) = A049000(n) - 10^n * (10^n + 1) / 2 + 2 ~ (Pi^2/12 - 1/2) * 10^(2*n). - _Amiram Eldar_, Feb 16 2020 %e A049030 For n = 1, the sum of sigma(j), for j < 10 is 0 + 0 + 0 + 2 + 0 + 5 + 0 + 6 + 3 = 16, so a(1) = 16. %Y A049030 Cf. A001065, A046915, A048050, A048995, A049000. %Y A049030 Cf. A072691 (Pi^2/12). %K A049030 base,nonn %O A049030 1,1 %A A049030 _Enoch Haga_ and _Jud McCranie_ %E A049030 More terms from _Amiram Eldar_, Feb 16 2020