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 A132999 #27 Sep 08 2022 08:45:31 %S A132999 1,2,3,4,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26, %T A132999 27,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50, %U A132999 51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69 %N A132999 Imperfect numbers: Not equal to sum of proper divisors. %C A132999 Imperfect numbers are either deficient numbers or abundant numbers. %D A132999 C. A. Pickover, El prodigio de los numeros, RBA Coleccionables, 2007, p. 190. %H A132999 Ivan Panchenko, <a href="/A132999/b132999.txt">Table of n, a(n) for n = 1..10000</a> %H A132999 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %F A132999 a(n) ~ n. - _Charles R Greathouse IV_, Feb 06 2015 %p A132999 with(numtheory): A132999:=n->`if`(sigma(n)=2*n,NULL,n): seq(A132999(n), n=1..100); # _Wesley Ivan Hurt_, Sep 11 2015 %o A132999 (PARI) is(n)=sigma(n,-1)!=2 \\ _Charles R Greathouse IV_, Feb 06 2015 %o A132999 (Magma) [n: n in [1..120] | not SumOfDivisors(n) eq 2*n]; // _Vincenzo Librandi_, Sep 12 2015 %Y A132999 Cf. A000396 (perfect numbers), A005100 (deficient numbers), A005101 (abundant numbers). %K A132999 easy,nonn %O A132999 1,2 %A A132999 _Omar E. Pol_, Oct 13 2007