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:

$1, 3, 6, 66, 3003, 66 \, 066, 617 \, 716, 3 \, 544 \, 453, 6 \, 172 \, 882 \, 716, \ldots$

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): $15$
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