OFFSET
0,1
LINKS
S. T. Thompson, Problem E754: Skew Ordered Sequences, Amer. Math. Monthly, 54 (1947), 416-417. [Annotated scanned copy]
FORMULA
a(0)=a(1)=2; thereafter a(n) = (1/4)*Sum_{k=1..n} binomial(n-1, k-1)*a(k-1)*a(n-k).
MAPLE
f:=proc(n) option remember;
if n <= 1 then 2 else (1/4)*add(binomial(n-1, k-1)*f(k-1)*f(n-k), k=1..n); fi;
end;
[seq(f(n), n=0..30)];
PROG
(Python)
from itertools import accumulate, islice
def A260786_gen(): # generator of terms
yield from (2, 2)
blist = (0, 2)
while True:
yield (blist := tuple(accumulate(reversed(blist), initial=0)))[-1]
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Aug 04 2015
STATUS
approved