Couples adjacent at an alternating round table

Around a circular table with $2n$ seats ($n>2$), $n$ husbands and their $n$ wives are seated at random, subject to men and women alternating. What is the expected number of couples in which the husband and wife sit next to each other?

$2$. Fix a husband's seat. Both of his neighbours are women, and his wife is equally likely to be in any of the $n$ women's seats, so she is next to him with probability $2/n$. Summing over $n$ couples gives $2$.