|
|
A156306
|
|
E.g.f.: A(x) = exp( Sum_{n>=1} sigma(n) * a(n-1)*x^n/n! ) = Sum_{n>=0} a(n)*x^n/n! with a(0)=1.
|
|
0
|
|
|
1, 1, 4, 26, 292, 3468, 69664, 1208936, 32822456, 858979216, 28933584112, 836115182512, 40673697842208, 1381857061152896, 67261437417875776, 3297904559465926208, 192628214559932492928, 8815748379077085483264
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
LINKS
|
|
|
FORMULA
|
a(n) = Sum_{k=1..n} sigma(k) * C(n-1,k-1)*a(k-1)*a(n-k) for n>0, with a(0)=1.
|
|
EXAMPLE
|
E.g.f: A(x) = 1 + x + 4*x^2/2! + 26*x^3/3! + 292*x^4/4! + 3468*x^5/5! +...
log(A(x)) = x + 3*1*x^2/2! + 4*4*x^3/3! + 7*26*x^4/4! + 6*292*x^5/5! + 12*3468*x^6/6! +...
|
|
PROG
|
(PARI) {a(n)=if(n==0, 1, n!*polcoeff(exp(sum(k=1, n, sigma(k)*a(k-1)*x^k/k!)+x*O(x^n)), n))}
(PARI) {a(n)=if(n==0, 1, sum(k=1, n, sigma(k)*binomial(n-1, k-1)*a(k-1)*a(n-k)))}
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|