cp's OEIS Frontend

A291109 Numbers that are not the sum of the squarefree divisors of some natural number.

%I A291109 #9 Jun 26 2018 06:36:02
%S A291109 2,5,7,9,10,11,13,15,16,17,19,21,22,23,25,26,27,28,29,31,33,34,35,37,
%T A291109 39,40,41,43,45,46,47,49,50,51,52,53,55,57,58,59,61,63,64,65,66,67,69,
%U A291109 70,71,73,75,76,77,78,79,81,82,83,85,86,87,88,89,91,92,93,94,95,97,99,100,101,103,105,106,107,109,111
%N A291109 Numbers that are not the sum of the squarefree divisors of some natural number.
%C A291109 Impossible values for A048250 (numbers k in increasing order such that A048250(m) = k has no solution).
%C A291109 Numbers that are not of the form Product (p_i + 1), p is a prime, so all odd numbers (except 1 and 3) are in this sequence.
%C A291109 Also numbers that are not the sum of the divisors of some squarefree number.
%H A291109 Robert Israel, <a href="/A291109/b291109.txt">Table of n, a(n) for n = 1..10000</a>
%H A291109 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%p A291109 sort(convert({$1..1000} minus map(numtheory:-sigma, select(numtheory:-issqrfree, {$1..1000})),list)); # _Robert Israel_, Jun 26 2018
%t A291109 TakeWhile[Complement[Range@ #, Union@ Table[Total@ Select[Divisors@ n, SquareFreeQ], {n, 2 #}]], Function[k, k <= #]] &@ 111
%Y A291109 Cf. A005114, A005117, A007369, A048250, A048995, A062822, A063948, A064000, A203444, A206778, A274793.
%K A291109 nonn
%O A291109 1,1
%A A291109 _Ilya Gutkovskiy_, Aug 17 2017