login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Odd noninfinitary abundant numbers: the odd terms of A348274.
5

%I #9 Oct 13 2021 10:31:43

%S 99225,1091475,1289925,1334025,1576575,1686825,1715175,1863225,

%T 1885275,2027025,2061675,2282175,2304225,2395575,2401245,2436525,

%U 2480625,2650725,2723175,2789325,2877525,2962575,3031875,3075975,3132675,3185325,3186225,3296475,3353805,3501225

%N Odd noninfinitary abundant numbers: the odd terms of A348274.

%C The number of terms below 10^k, for k = 5, 6, ..., are 1, 113, 630, 7771, 73685, ... Apparently this sequence has an asymptotic density 0.000007...

%H Amiram Eldar, <a href="/A348275/b348275.txt">Table of n, a(n) for n = 1..10000</a>

%e 99225 is a term since A348271(99225) = 107207 > 99225.

%t f[p_, e_] := Module[{b = IntegerDigits[e, 2], m}, m = Length[b]; Product[If[b[[j]] > 0, 1 + p^(2^(m - j)), 1], {j, 1, m}]]; isigma[1] = 1; isigma[n_] := Times @@ f @@@ FactorInteger[n]; s[n_] := DivisorSigma[1,n] - isigma[n]; Select[Range[1, 2*10^6, 2], s[#] > # &]

%Y Cf. A348271.

%Y Subsequence of A005231 and A348274.

%Y Similar sequences: A094889, A127666, A129485, A293186, A321147.

%K nonn

%O 1,1

%A _Amiram Eldar_, Oct 09 2021