|
|
A079798
|
|
Partition of positive integers into shortest possible groups, starting with (1), (2,3), (4,5,6), (7,8,9,10,11), such that a(n) = the sum of the terms of the n-th group is a multiple of a(n-1) and a(n) > a(n-1).
|
|
5
|
|
|
1, 5, 15, 45, 495, 16830, 4358970, 1159486020, 196818113950920, 3151092455396895169036800, 136084696980410308844836382925537725529600, 9996588705394796239042140065772174939073840705818917941136700639014745600
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Dropping requirement a(n) > a(n-1) leads to a different partition: (1), (2, 3), (4, 5, 6), (7, 8), ... - see A160275.
For partition starting with (1), (2), (3,4,5), see A075631.
|
|
LINKS
|
|
|
FORMULA
|
|
|
PROG
|
(PARI) A000217(n)= { return(n*(n+1)/2) ; } upto(first, osum, strict)= { local(trifirst, tstsu) ; trifirst=A000217(first-1) ; for(lst=first+1, first+100000000, tstsu=A000217(lst)-trifirst ; if(strict==1 && tstsu<= osum, next ; ) ; if( tstsu % osum == 0, return(lst) ; ) ; ) ; return(-1) ; } { a=1 ; first=2 ; for(n=2, 40, last=upto(first, a, 1) ; a=A000217(last)-A000217(first-1) ; print(a, ", ") ; first=last+1 ; ) ; - R. J. Mathar, May 06 2006
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|