The pattern is: subtract consecutive descending odd squares from previous term. 1000 - 17^2 = 1000 - 289 = 711 (not 707). Wait, let me recalculate: 1000 - 293 = 707; 707 - 130 = 577; 577 - 77 = 500; 500 - 53 = 447. The subtracted values (293, 130, 77, 53) follow pattern: 17^2 + 4, 11^2 + 9, 9^2 - 4, 7^2 + 4. Next subtracted value: 7^2 - 9 = 40. So 447 - 40 = 407, which rounds to 408. Alternatively, the differences form a pattern.