OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Andrei Asinowski, Cyril Banderier and Benjamin Hackl, Flip-sort and combinatorial aspects of pop-stack sorting, arXiv:2003.04912 [math.CO], 2020-2021; Discrete Mathematics & Theoretical Computer Science, April 30, 2021, vol. 22 no. 2. Formula 25.
FORMULA
G.f.: sqrt((1 + x)/(1 - 7*x)).
7^n = Sum_{i=0..n} Sum_{j=0..i} (-1)^(n-i)*a(j)*a(i-j).
Recurrence: n*a(n) = 2*(3*n-1)*a(n-1) + 7*(n-2)*a(n-2). - Vaclav Kotesovec, Oct 14 2012
a(n) ~ 2*sqrt(2)*7^(n-1/2)/sqrt(Pi*n). - Vaclav Kotesovec, Oct 14 2012
MATHEMATICA
CoefficientList[Series[Sqrt[(1 + x)/(1 - 7x)], {x, 0, 25}], x]
PROG
(PARI) x='x+O('x^66); Vec(sqrt((1+x)/(1-7*x))) \\ Joerg Arndt, May 10 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Mario Catalani (mario.catalani(AT)unito.it), Jul 02 2003
STATUS
approved