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A048015
Number of nonempty subsets of {1,2,...,n} in which exactly 5/6 of the elements are <= (n-1)/3.
1
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 12, 13, 78, 84, 90, 315, 336, 357, 952, 1008, 1064, 2394, 2520, 2646, 5502, 5775, 6049, 13409, 14124, 14850, 39600, 42042, 44550, 135135, 144144, 153439, 464464, 495495, 527527
OFFSET
1,16
LINKS
MAPLE
f:= proc(n) local k, m;
m:= floor((n-1)/3);
add(binomial(m, 5*k/6)*binomial(n-m, k/6), k=6..m*6/5, 6);
end proc:
map(f, [$1..100]); # Robert Israel, Jul 23 2018
CROSSREFS
Sequence in context: A111019 A306583 A048035 * A061082 A231870 A231874
KEYWORD
nonn
STATUS
approved