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A256259 Sum of divisors of the minimal numbers (A007416).

%I A256259 #22 Nov 23 2020 07:55:51
%S A256259 1,3,7,12,28,31,60,91,124,168,127,360,403,546,508,744,1170,1651,2418,
%T A256259 2880,2821,3048,2047,4368,3751,5952,9360,9906,8188,12493,8191,19344,
%U A256259 15367,22568,22506,24384,28800,26611,39312,32764,51181,59520,49128,79248,99944,92202,112320,116281,106483,160797
%N A256259 Sum of divisors of the minimal numbers (A007416).
%C A256259 Has a symmetric representation in the same way as A000203 and all its subsequences.
%H A256259 Amiram Eldar, <a href="/A256259/b256259.txt">Table of n, a(n) for n = 1..10000</a> (calculated from the b-file at A007416)
%F A256259 a(n) = A000203(A007416(n)).
%t A256259 (* The d-th element in list minDiv[n, b] is the smallest numbers k<=n with exactly d<=b divisors, otherwise it is zero. Computation stops as soon as either inequality fails. *)
%t A256259 minDiv[n_, b_] :=
%t A256259 Module[{list = Array[0 &, b], k = 1, d},
%t A256259   While[k <= n, d = DivisorSigma[0, k];
%t A256259    If[d <= b && list[[d]] == 0, list[[d]] = k];
%t A256259    If[d <= b, k++, k = n + 2]]; list]
%t A256259 a256259[n_, b_] :=
%t A256259 Map[DivisorSigma[1, #] &, Sort[Select[minDiv[n, b], # != 0 &]]]
%t A256259 a256259[100000, 300] (* computes the first 60 elements of the sequence *)
%t A256259 (* _Hartmut F. W. Hoft_, Apr 27 2015 *)
%Y A256259 Cf. A000203, A005179, A007416, A007626, A053212, A063072, A081533, A237271, A237593.
%K A256259 nonn
%O A256259 1,2
%A A256259 _Omar E. Pol_, Apr 20 2015