A031547 Numbers n such that continued fraction for sqrt(n) has even period and central term 49.

2403, 2411, 2423, 2427, 2447, 2459, 2467, 2471, 2503, 2531, 2539, 2543, 2547, 2551, 2563, 2571, 2579, 2591, 2599, 9608, 9696, 9704, 9728, 9760, 9824, 9832, 9856, 9888, 9896, 9920, 9928, 9984, 10016, 10048, 10080, 10088, 10144, 10208, 10216, 10240