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The number of powerful abundant numbers (A363169) not exceeding 10^n.
1

%I #5 May 19 2023 06:14:54

%S 0,3,23,82,297,1000,3268,10534,33799,107901,343155,1090189,3460380,

%T 10970774,34749182,109991778,348006756,1101058505,3483105232,

%U 11017518803

%N The number of powerful abundant numbers (A363169) not exceeding 10^n.

%C The ratios a(n)/A118896(n) seem to converge to a positive value as n grows: for n = 14..20 they are 0.506417..., 0.506728..., 0.506863..., 0.506890..., 0.506987..., 0.507059..., 0.507120... .

%C Conjecture: the asymptotic relative density of the abundant numbers within the powerful numbers exists and equals 0.507... .

%e a(2) = 3 since there are 3 powerful abundant numbers not exceeding 10^2: 36, 72 and 100.

%t seq[nmax_] := Module[{c = 0, p = 10, k = 1, kmax = 10^nmax, s = {}}, While[k <= kmax, If[DivisorSigma[-1, k] > 2 && Min[FactorInteger[k][[;;, 2]]] > 1, c++]; If[k == p, AppendTo[s, c]; p *= 10]; k++]; s]; seq[5]

%o (PARI) is(n) = { my(f = factor(n)); n > 1 && vecmin(f[, 2]) > 1 && sigma(f, -1) > 2; } \\ A363169

%o lista(nmax) = {my(c = 0, p = 10, k = 1, kmax = 10^nmax); while(k <= kmax, if(is(k), c++); if(k == p, print1(c, ", "); p *= 10); k++); }

%Y Cf. A001694, A005101, A118896, A302992, A363169.

%K nonn,more

%O 1,2

%A _Amiram Eldar_, May 19 2023