A334408 - OEIS

A334408

Numbers k whose unitary divisors can be partitioned into two disjoint sets with equal sum, such that if d is in one set, then k/d is in the other set.

462, 858, 870, 1482, 2310, 2730, 3570, 3990, 4002, 4290, 4620, 4830, 5460, 5610, 6006, 6090, 6270, 6438, 6510, 6630, 6930, 7140, 7410, 7770, 7854, 7998, 8190, 8580, 8610, 8778, 8970, 9240, 9570, 9660, 9870, 10010, 10230, 10374, 10626, 10920, 11220, 11310, 11550

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

The squarefree terms of A334407 are also terms of this sequence. Terms that are not squarefree are 4620, 5460, 6930, 7140, 8190, 8580, 9240, 9660, ...

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..680

EXAMPLE

462 is a term since its set of unitary divisors can be partitioned into two disjoint subsets: {1, 11, 14, 22, 66, 77, 154, 231} and {462, 42, 33, 21, 7, 6, 3, 2} = {462/1, 462/11, 462/14, 462/22, 462/66, 462/77, 462/154, 462/231} with the equal sum of 576, and with no pair of complementary unitary divisors (d, 462/d) in the same subset.

MATHEMATICA

seqQ[n_] := Module[{d = Select[Divisors[n], CoprimeQ[#, n/#] &]}, nd = Length[d]; divpairs = d[[-1 ;; nd/2 + 1 ;; -1]] - d[[1 ;; nd/2]]; sd = Plus @@ divpairs; If[OddQ[sd], False, SeriesCoefficient[Series[Product[1 + x^divpairs[[i]], {i, Length[divpairs]}], {x, 0, sd/2}], sd/2] > 0]]; Select[Range[2, 10000], seqQ]

CROSSREFS

Subsequence of A290466.

Cf. A077610, A334407.

Sequence in context: A104397 A108749 A267740 * A254468 A242321 A222342

Adjacent sequences: A334405 A334406 A334407 * A334409 A334410 A334411

KEYWORD

nonn

AUTHOR

Amiram Eldar, Apr 27 2020

STATUS

approved