Palindromic Triangular Numbers whose Index is Palindromic
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Sequence of Palindromic Triangular Numbers with Palindromic Indices
The sequence of palindromic triangular numbers whose indices are also palindromic begins:
- $1, 3, 6, 66, 3003, 66 \, 066, 617 \, 716, 3 \, 544 \, 453, 6 \, 172 \, 882 \, 716, \ldots$
This sequence is A003098 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).
Their indices are:
- $1, 2, 3, 11, 77, 363, 1111, 2662, 111 \, 111, \ldots$
This sequence is A008510 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $15$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $15$