A083829 Palindromes n such that 3n + 1 is also a palindrome.

1, 2, 7, 77, 141, 151, 161, 242, 252, 262, 777, 7777, 14041, 14141, 14241, 15051, 15151, 15251, 16061, 16161, 16261, 24042, 24142, 24242, 25052, 25152, 25252, 26062, 26162, 26262, 77777, 777777, 1404041, 1405041, 1406041, 1414141, 1415141