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 A088820 #30 Mar 11 2025 04:39:35 %S A088820 22,56,130,184,368,836,1012,2272,11096,17816,18904,33664,45356,70564, %T A088820 77744,85936,91388,100804,128768,254012,388076,391612,527872,1090912, %U A088820 2087936,2291936,13174976,17619844,29465852,35021696,45335936,120888092,260378492,381236216 %N A088820 Numbers k with abundance radius of 8, i.e., abs(sigma(k)-2*k) = 8. %C A088820 Original definition: Abundance-radius=8, that is Abs[sigma[n]-2n]=8 (either +8 or -8). A045770 from 3rd term complemented by -8 cases. %H A088820 Amiram Eldar, <a href="/A088820/b088820.txt">Table of n, a(n) for n = 1..66</a> (terms below 10^18, from the b-files at A088833 and A125247) %e A088820 22 is in the sequence since sigma(22) = 1 + 2 + 11 + 22 = 36 = 2*22 - 8. %e A088820 56 is in the sequence since sigma(56) = 1 + 2 + 4 + 7 + 8 + 14 + 28 + 56 = 120 = 2*56 + 8. - _Michael B. Porter_, Jul 20 2016 %t A088820 Select[Range[1, 10^6], Abs[DivisorSigma[1, #] - 2 #] == 8 &] (* _Vincenzo Librandi_, Jul 20 2016 *) %o A088820 (PARI) is(n)=abs(sigma(n)-2*n)==8 \\ Use, e.g., select(is,[1..10^5]*2). - _M. F. Hasler_, Jul 19 2016 %o A088820 (Magma) [n: n in [1..2*10^7] | Abs(DivisorSigma(1, n) - 2*n) eq 8]; // _Vincenzo Librandi_, Jul 20 2016 %Y A088820 Disjoint union of A088833 (abundance 8) and A125247 (deficiency 8). %Y A088820 Cf. A045770, A045768, A055708, A077374, A088007, A088008, A088010, A088011, A088012, A088818, A088819. %Y A088820 Cf. A000203 (sigma), A033880 (abundance), A005100 (deficient numbers). %K A088820 nonn %O A088820 1,1 %A A088820 _Labos Elemer_, Oct 20 2003 %E A088820 More terms from _David Wasserman_, Aug 18 2005 %E A088820 Edited by _M. F. Hasler_, Jul 19 2016 %E A088820 a(33)-a(34) from _Amiram Eldar_, Mar 11 2025