[go: up one dir, main page]

login
A348824
Numbers in array A327259 that do not have a unique decomposition into numbers of A327261.
1
32, 48, 72, 96, 112, 126, 128, 144, 160, 168, 176, 192, 198, 221, 224, 240, 252, 256, 264, 288, 294, 304, 336, 342, 347, 352, 360, 368, 384, 392, 396, 414, 416, 432, 448, 456, 462, 480, 496, 504, 512, 528, 544, 545, 552, 558, 560, 576, 588, 599
OFFSET
1,1
COMMENTS
While array A327259 has many properties of the multiplication table, one way the numbers that sieve out of the array fail to be prime numbers is that unique factorization does not hold. Some numbers have two or more decompositions.
For i >= 2, A327259(i, a(n)) is in the sequence.
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..1256 (all terms m <= 10000)
EXAMPLE
48 is in the sequence because 48 = A327259(2,12) = A327259(4,6) and 2, 4, 6 and 12 are in A327261.
72 is in the sequence because 72 = A327259(2,2,5) = A327259(6,6) and 2, 5 and 6 are in A327261. A327259(2,2,5) is well-defined because A327259(n,k) is associative.
221 is in the sequence because 221 = A327259(5,25) = A327259(11,11) and 5, 11 and 25 are in A327261.
462 is in the sequence because 462 = A327259(6,39) = A327259(11,22) = A327259(14,17) and 6, 11, 14, 17, 22 and 39 are in A327261.
The first six terms and their decompositions:
1 32 = A327259(2,2,2) = A327259(4,4)
2 48 = A327259(2,12) = A327259(4,6)
3 72 = A327259(2,2,5) = A327259(6,6)
4 96 = A327259(2,2,6) = A327259(4,12)
5 112 = A327259(2,28) = A327259(4,14)
6 126 = A327259(5,14) = A327259(6,11)
More in a-file.
MATHEMATICA
T[n_, k_]:=2n*k-If[Mod[n, 2]==1, If[Mod[k, 2]==1, n+k-1, k], If[Mod[k, 2]==1, n, 0]]; F[d_]:=If[(q=Union[Sort/@(Position[Table[T[n, k], {n, 2, Ceiling[d/3]}, {k, 2, Ceiling[d/3]}], d]+1)])=={}, {{d}}, q]; FC[x_]:=FixedPoint[Union[Sort/@Flatten[Flatten/@Tuples[#]&/@((F/@#&/@#)&[#]), 1]]&, F[x]]; list={}; Do[If[Length@FC@i>1, AppendTo[list, i]], {i, 300}]; list (* Giorgos Kalogeropoulos, Nov 05 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
David Lovler, Oct 31 2021
EXTENSIONS
Name amended by David Lovler, Jan 26 2022
STATUS
approved