OFFSET
0,3
COMMENTS
Grows asymptotically as O(n^(8n)) (Fredman 1976).
LINKS
Michael L. Fredman (1976). "How good is the information theory bound in sorting?". Theoretical Computer Science. 1 (4): 355-361.
Wikipedia, X+Y sorting.
FORMULA
a(n) = Sum_{i=0..2*n} binomial(2*binomial(n,2)^2 + 2*binomial(n,2), i).
EXAMPLE
For n=2, 2*binomial(n,2)^2 + 2*binomial(n,2) = 4 and binomial(4,0) + ... + binomial(4,2*n) = 16, so a(2)=16.
CROSSREFS
KEYWORD
nonn
AUTHOR
David Eppstein, Apr 08 2021
STATUS
approved