249×250-250×251+251×252-252×253+253×254-254×255

249 * 250 - 250 * 251 + 251 * 252 - 252 * 253 + 253 * 254 - 254 * 255 = -1512;

249 * 250 = 62 250;

250 * 251 = 62 750;

62 250 - 62 750 = -500;

251 * 252 = 63 252;

-500 + 63 252 = 62 752;

252 * 253 = 63 756;

62 752 - 63 756 = -1004;

253 * 254 = 64 262;

-1004 + 64 262 = 63 258;

254 * 255 = 64 770;

63 258 - 64 770 = -1512.