|
| |
|
|
A127782
|
|
G.f. satisfies: A(x) = 1 + x*A(x+x^2).
|
|
6
| |
|
|
1, 1, 1, 2, 4, 11, 33, 114, 438, 1845, 8458, 41823, 221539, 1250269, 7481758, 47278652, 314374316, 2192798077, 16000160519, 121831654450, 965946444587, 7958739329386, 68023023892680, 602115897105136, 5511499584735858
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,4
|
|
|
COMMENTS
| Equals eigensequence of triangle A026729 [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Jan 16 2009]
|
|
|
LINKS
| P. Barry, Invariant number triangles, eigentriangles and Somos-4 sequences, Arxiv preprint arXiv:1107.5490, 2011.
|
|
|
FORMULA
| a(n) = Sum_{k=0..[n/2]} C(n-k,k)*a(n-k-1) for n>0 with a(0)=1.
|
|
|
PROG
| (PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=0, n, A=1+x*subst(A, x, x+x^2)); polcoeff(A, n)} (PARI) a(n)=if(n==0, 1, sum(k=0, n\2, binomial(n-k, k)*a(n-k-1)))
|
|
|
CROSSREFS
| A026729 [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Jan 16 2009]
Sequence in context: A025191 A192405 A035354 * A002846 A188478 A123444
Adjacent sequences: A127779 A127780 A127781 * A127783 A127784 A127785
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Jan 28 2007
|
| |
|
|
