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 A186889 #15 Jan 30 2013 02:55:58 %S A186889 6,18,20,100,1888,2044928,33099776,35021696,45335936,533020672 %N A186889 Oex perfect numbers: n such that A186644(n) = 2*n. %C A186889 There are no squarefree infinitary perfect numbers > 6 (cf. A007357). Therefore, the second and all further terms of the sequence are infinitary deficient (A129657). %C A186889 No further term between 1888 and 1440000. - R. J. Mathar, Mar 18 2011 %C A186889 a(11) > 3*10^10. 1471763808896 is also a term. - _Donovan Johnson_, Jan 30 2013 %e A186889 Let n = 100 with divisors 1, 2, 4, 5, 10, 20, 25, 50, and 100. By the definition in A186643, only 1, 4, 20, 25, 50, 100 among these are oex divisors. Since 1+4+20+25+50+100 = 2*100, 100 is in the sequence. %o A186889 (PARI) for(n=4, 10^9, if(isprime(n), next); d=divisors(n); s=n+1; for(j=2, numdiv(n)-1, for(k=2, 30, if(n%d[j]^k<>0, if(k%2==0, s=s+d[j]); k=30))); if(s==2*n, print(n))) /* _Donovan Johnson_, Jan 28 2013 */ %Y A186889 Cf. A186443, A186444, A129657, A000396, A007357. %K A186889 nonn %O A186889 1,1 %A A186889 _Vladimir Shevelev_, Feb 28 2011 %E A186889 a(6)-a(10) from _Donovan Johnson_, Jan 28 2013