Palindromic Triangular Numbers whose Index is Palindromic

Sequence of Palindromic Triangular Numbers with Palindromic Indices
The sequence of palindromic triangular numbers whose indices are also palindromic begins:
 * $1, 3, 6, 66, 3003, 66 \, 066, 617 \, 716, 3 \, 544 \, 453, 6 \, 172 \, 882 \, 716, \ldots$

Their indices are:
 * $1, 2, 3, 11, 77, 363, 1111, 2662, 111 \, 111, \ldots$