|
|
A261799
|
|
Number of 7-compositions of n: matrices with 7 rows of nonnegative integers with positive column sums and total element sum n.
|
|
2
|
|
|
1, 7, 77, 819, 8687, 92141, 977347, 10366833, 109962202, 1166381804, 12371946734, 131230670312, 1391978902090, 14764881252772, 156612803600094, 1661210126351328, 17620647995924820, 186904251828901124, 1982515022137687464, 21028766197355391048
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
Also the number of compositions of n where each part i is marked with a word of length i over a septenary alphabet whose letters appear in alphabetical order.
|
|
LINKS
|
|
|
FORMULA
|
G.f.: (1-x)^7/(2*(1-x)^7-1).
|
|
MAPLE
|
a:= proc(n) option remember; `if`(n=0, 1,
add(a(n-j)*binomial(j+6, 6), j=1..n))
end:
seq(a(n), n=0..20);
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|