  A binary partition of a positive integer $n$ is a partition of $n$ in which
each part has size a power of two. In this note we first construct a Gray
sequence on the set of binary partitions of $n$. This is an ordering of the set
of binary partitions of each $n$ (or of all $n$) such that adjacent partitions
differ by one of a small set of elementary transformations; here the allowed
transformatios are replacing $2^k+2^k$ by $2^{k+1}$ or vice versa (or addition
of a new +1). Next we give a purely local condition for finding the successor
of any partition in this sequence; the rule is so simple that successive
transitions can be performed in constant time. Finally we show how to compute
directly the bijection between $k$ and the $k$th term in the sequence.
  This answers a question posed by Donald Knuth in section 7.2.1 of The Art of
Computer Programming.

Combinatorics