2178

Number
$2178$ (two thousand, one hundred and seventy-eight) is:
 * $2 \times 3^2 \times 11^2$


 * The $2$nd of only $2$ numbers with $4$ digits or less which has a multiple which is its reversal:
 * $2178 \times 4 = 8712$


 * A $4$-th order recurring digital invariant:
 * $2^4 + 1^4 + 7^4 + 8^4 = 6514$; $6^4 + 5^4 + 1^4 + 4^4 = 2178$