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 A064599 #20 Sep 07 2024 15:39:32
%S A064599 4,9,18,24,25,49,112,121,169,289,361,529,841,961,1369,1681,1849,1984,
%T A064599 2209,2809,3481,3721,4489,5041,5329,6241,6889,7921,9409,10201,10609,
%U A064599 11449,11881,12769,16129,17161,18769,19321,22201,22801,24649,26569
%N A064599 The sum of the nonunitary divisors of n is a divisor of n; i.e., sigma(n) - usigma(n) divides n.
%C A064599 The sequence consists of the nonunitary perfect numbers (A064591), squares of primes (A001248) and 18.
%H A064599 Amiram Eldar, <a href="/A064599/b064599.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harry J. Smith)
%t A064599 nusigma[ n_ ] := DivisorSigma[ 1, n ]-Times@@(1+Power@@#&/@FactorInteger[ n ]); For[ n=1, True, n++, v=nusigma[ n ]; If[ v>0&&Mod[ n, v ]==0, Print[ n ] ] ]
%o A064599 (PARI) usigma(n)= { local(f,s=1); f=factor(n); for(i=1, matsize(f)[1], s*=1 + f[i, 1]^f[i, 2]); return(s) }
%o A064599 { n=0; for (m=1, 10^9, v=sigma(m) - usigma(m); if (v>0 && m%v == 0, write("b064599.txt", n++, " ", m); if (n==1000, break)) ) } \\ _Harry J. Smith_, Sep 19 2009
%Y A064599 Cf. A048146, A064591.
%K A064599 nonn,easy
%O A064599 1,1
%A A064599 _Dean Hickerson_, Sep 25 2001