A028503 Numbers n such that n(n+2) is a palindrome.

1, 2, 9, 17, 23, 64, 75, 99, 191, 204, 999, 1747, 1907, 2365, 2966, 5731, 9999, 18991, 20564, 99999, 174601, 174747, 179317, 243063, 293786, 552101, 999999, 1868287, 2967032, 9200156, 9999999, 22765895, 31552659, 93809716