J. Brudern et al., ON THE EXPONENTIAL SUM OVER K-FREE NUMBERS, Philosophical transactions-Royal Society of London. Physical sciences and engineering, 356(1738), 1998, pp. 739-761
This paper is concerned with mean values of exponential sum generating
functions over k-free numbers, and especially their L-1-means. We als
o provide non-trivial estimates for the L-2-means of such generating f
unctions restricted to the minor arcs occurring in Hardy-Littlewood di
ssections, thereby permitting the circle method to be successfully app
lied to certain additive problems hitherto beyond its reach.