|
|
A120578
|
|
Irregular array where the n-th row are the divisors, not occurring earlier in the sequence, of the sum of the terms in all previous rows. a(1)=4.
|
|
3
|
|
|
4, 1, 2, 7, 14, 28, 8, 56, 3, 5, 6, 10, 12, 15, 20, 24, 30, 40, 60, 120, 31, 93, 155, 465, 13, 39, 403, 1209, 17, 169, 221, 2873, 21, 293, 879, 2051, 6153, 25, 50, 311, 622, 1555, 3110, 7775, 15550, 37, 43, 74, 86, 148, 172, 259, 301, 518, 602, 1036, 1204, 1591
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Is this sequence a permutation of the positive integers?
|
|
LINKS
|
|
|
EXAMPLE
|
Array begins:
4
1,2
7
14
28
8,56
Now these terms add up to 120. So row 7 is the divisors of 120 which do not occur earlier in the sequence. 1,2,4 and 8 occur in earlier rows, so row 7 is (3,5,6,10,12,15,20,24,30,40,60,120).
|
|
MATHEMATICA
|
f[t_] := Flatten[Append[t, Select[Divisors[Plus @@ t], FreeQ[t, # ] &]]]; Nest[f, {4}, 12] (* Ray Chandler, Jun 17 2006 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,tabf
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|