66,056,806,460,865,066

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Number

$66 \, 056 \, 806 \, 460 \, 865 \, 066$ is:

$2 \times 3 \times 7 \times 11 \times 1367 \times 6043 \times 17 \, 308 \, 303$

The $13$th palindromic triangular number after $0$, $1$, $3$, $6$, $66$, $3003$, $66 \, 066$, $617 \, 716$, $3 \, 544 \, 453$, $6 \, 172 \, 882 \, 716$, $30 \, 416 \, 261 \, 403$, $61 \, 728 \, 399 \, 382 \, 716$ whose index is itself palindromic:

$66 \, 056 \, 806 \, 460 \, 865 \, 066 = T_{363 \, 474 \, 363}$

The $363 \, 474 \, 363$rd triangular number:

$66 \, 056 \, 806 \, 460 \, 865 \, 066 = \ds \sum_{k \mathop = 1}^{363 \, 474 \, 363} k = \dfrac {363 \, 474 \, 363 \times \paren {363 \, 474 \, 363 + 1} } 2$

Also see

• Previous  ... Next: Palindromic Triangular Numbers with Palindromic Index
• Previous  ... Next: Triangular Number

Sources

• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $363,474,363$