login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A047196 Number of nonempty subsets of {1,2,...,n} in which exactly 1/4 of the elements are <= n/3. 1
0, 0, 0, 1, 4, 8, 20, 41, 63, 126, 252, 392, 844, 1780, 2800, 5995, 12545, 19595, 41951, 88634, 138866, 299411, 636524, 997640, 2154104, 4594244, 7201692, 15584085, 33355944, 52311408, 113406028, 243374923, 381766253, 828748052 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Robert Israel, Table of n, a(n) for n = 1..2000

FORMULA

a(n) = Sum_{1<=j<=n/4} binomial(floor(n/3),j)*binomial(n-floor(n/3),3*j). - Robert Israel, Dec 15 2020

MAPLE

f:= proc(n) local t, k;

add(binomial(floor(n/3), k)*binomial(n-floor(n/3), 3*k), k=1..n/4)

end proc:

map(f, [$1..50]); # Robert Israel, Dec 15 2020

CROSSREFS

Sequence in context: A301138 A008136 A254128 * A009889 A334706 A095804

Adjacent sequences:  A047193 A047194 A047195 * A047197 A047198 A047199

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 18 17:32 EDT 2021. Contains 345120 sequences. (Running on oeis4.)