OFFSET
0,5
COMMENTS
Or number of permutations p of [n] having exactly four pairs (i,j) in {1,...,n} X {1,...,floor(log_2(i))} such that p(i) > p(floor(i/2^j)).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..200
Eric Weisstein's World of Mathematics, Heap
Wikipedia, Binary heap
Wikipedia, Permutation
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 13 2019
STATUS
approved