Amazon is laying off more than 18,000 employees — a significantly bigger number than previously planned — in the latest sign that a technology slump is deepening. Chief Executive Officer Andy Jassy announced the move in a memo to staff Wednesday, saying it followed the company's annual planning process. The cuts, which began last year, were previously expected to affect about 10,000 people. The reduction is concentrated in the firm's corporate ranks, mostly Amazon's retail division and human resources functions like recruiting.