The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A119366 Number of rooted planar n-trees whose number of leaves is equal to 1 modulo 3. 3
 0, 1, 1, 1, 2, 11, 51, 177, 519, 1513, 5042, 18866, 71270, 257974, 905425, 3193737, 11578842, 42930441, 159998493, 593445318, 2194106568, 8138471667, 30399156174, 114219616809, 430344635913, 1622777285682, 6125465491551 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS a(n)+A119365(n)+A119367(n)=A000108(n). LINKS Table of n, a(n) for n=0..26. FORMULA a(n)=sum{k=0..n, if(mod(n-k,3)=1, (1/n)*C(n,k)*C(n,k+1), 0)} a(0)=0, a(n)=sum{k=0..floor(n/3), (1/n)*C(n,3k+1)C(n,3k)},n>0; - Paul Barry, Jan 25 2007 MAPLE A119366 := proc(n) if n = 0 then 0; else add(binomial(n, 3*k+1)*binomial(n, 3*k), k=0..n/3) ; %/n ; end if; end proc: # R. J. Mathar, Dec 02 2014 CROSSREFS Sequence in context: A137960 A018933 A116586 * A034574 A054665 A134963 Adjacent sequences: A119363 A119364 A119365 * A119367 A119368 A119369 KEYWORD easy,nonn AUTHOR Paul Barry, May 16 2006 STATUS approved

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

Last modified August 9 15:15 EDT 2024. Contains 375044 sequences. (Running on oeis4.)