cp's OEIS Frontend

A307222 Deficient numbers k at least one of whose divisors is the sum of other distinct divisors of k.

%I A307222 #11 Jul 21 2021 00:42:52
%S A307222 45,63,99,105,110,117,130,135,154,165,170,182,189,195,225,231,238,255,
%T A307222 266,273,285,286,297,315,322,345,351,357,374,385,399,405,418,429,441,
%U A307222 455,459,475,483,494,495,506,513,525,561,567,585,595,598,609,621,627,646
%N A307222 Deficient numbers k at least one of whose divisors is the sum of other distinct divisors of k.
%C A307222 Erdős used the term "integers with the property P" for numbers k such that all the 2^d(k) sums formed from the d(k) divisors of k are distinct and proved that they are all deficient numbers and have a positive density. This sequence lists deficient numbers not having this property.
%C A307222 Differs from A051773 from n >= 12.
%H A307222 S. J. Benkoski and P. Erdős, <a href="https://doi.org/10.1090/S0025-5718-1974-0347726-9">On weird and pseudoperfect numbers</a>, Math. Comp., 28 (1974), pp. 617-623. <a href="http://www.renyi.hu/~p_erdos/1974-24.pdf">Alternate link</a>; <a href="https://doi.org/10.1090/S0025-5718-1975-0360452-6">1975 corrigendum</a>
%H A307222 Paul Erdős, <a href="http://www.renyi.hu/~p_erdos/1970-21.pdf">Some extremal problems in combinatorial number theory</a>, Mathematical Essays Dedicated to A. J. Macintyre, Ohio Univ. Press, Athens, Ohio (1970), pp. 123-133.
%e A307222 45 is in this sequence since its divisors are 1, 3, 5, 9, 15, 45 whose sum is 78 < 90, and thus it is deficient, yet the divisor 15 is the sum of other divisors of 45: 1 + 5 + 9.
%t A307222 T[n_, k_] := Module[{d = Divisors[n]}, SeriesCoefficient[Series[Product[1 + x^d[[i]], {i, Length[d]}], {x, 0, k}], k]]; seqQ[n_] := DivisorSigma[1, n] < 2n && Max[T[n, #] & /@ Range[DivisorSigma[1, n]]] > 1; Select[Range[1000], seqQ]
%Y A307222 Cf. A000005, A005100, A051773, A119347.
%K A307222 nonn
%O A307222 1,1
%A A307222 _Amiram Eldar_, Mar 29 2019