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 A129087 #7 Jun 05 2018 04:41:51 %S A129087 11025,34155,38745,39585,41895,75735,85995,99225,118755,131355,135135, %T A129087 193725,208845,218025,237195,241395,241605,245385,255645,271215, %U A129087 272745,275625,276885,279279,306495,307125,323505,342225,347985,364455,377685 %N A129087 Odd doubly abundant numbers (A125639). %C A129087 This sequence contains the odd members of A125639, which (empirically) accounts for only about 0.08% of them. %H A129087 Robert Israel, <a href="/A129087/b129087.txt">Table of n, a(n) for n = 1..1000</a> %F A129087 Odd numbers k, such that both k and s(k) (A001065) are abundant (A005101). %e A129087 The third odd number which is doubly abundant is 38745. Hence a(3)=38745. %p A129087 filter:= proc(n) local s; %p A129087 s:= numtheory:-sigma(n)-n; %p A129087 s > n and numtheory:-sigma(s)>2*s %p A129087 end proc: %p A129087 select(filter, [seq(i,i=3..400000,2)]); # _Robert Israel_, Jun 04 2018 %t A129087 s[n_]:=DivisorSigma[1,n]-n;DoublyAbundantNumberQ[k_]:=If[s[k]>k && s[s[k]]>s[k],True,False];Select[Range[500000],OddQ[ # ] && DoublyAbundantNumberQ[ # ] & ] %o A129087 (PARI) isok(n) = (n%2) && ((s=sigma(n)-n) > n) && (sigma(s) > 2*s); \\ _Michel Marcus_, Jun 05 2018 %Y A129087 Cf. A125639, A001065, A005101. %K A129087 easy,nonn %O A129087 1,1 %A A129087 _Ant King_, Apr 02 2007