|
| |
|
|
A137635
|
|
a(n) = Sum_{k=0..n} C(2k,k)*C(2k,n-k) ; equals row 0 of square array A137634.
|
|
4
| |
|
|
1, 2, 10, 46, 226, 1136, 5810, 30080, 157162, 826992, 4376408, 23267332, 124179570, 664919780, 3570265000, 19216805476, 103652442922, 560127574340, 3031887311256, 16435458039076, 89213101943000, 484839755040768
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,2
|
|
|
FORMULA
| G.f.: A(x) = 1/sqrt(1 - 4x(1+x)^2).
|
|
|
PROG
| (PARI) {a(n)=sum(k=0, n, binomial(2*k, k)*binomial(2*k, n-k))} /* Using the g.f.: */ {a(n)=polcoeff(1/sqrt(1-4*x*(1+x +x*O(x^n))^2), n, x)}
|
|
|
CROSSREFS
| Cf. A137634, A137636, A137637, A137638, A073157.
Sequence in context: A106709 A137193 A006213 * A029706 A191644 A009640
Adjacent sequences: A137632 A137633 A137634 * A137636 A137637 A137638
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Jan 31 2008
|
| |
|
|
