3,816

[Math.]  Each ratio, 45792/3816 = 73548/6129 = 89532/7461 = 91584/7632 = 12, uses each of 9 digits 1-9 once.

 

3,828

[Math.]  A triangular number (sum of all integers from 1 to 87): 3828 = 1+2+…+86+87.

 

3,843

[Math.]  Two multiples of number 3843, 3843×7 = 26,901 and 3843×9 = 34,587, use each of 10 digits 0-9 once.

 

3,849

[Math.]  38492 = 14,814,801.

 

3,852

[Math.]  9,949,716 = 2583×3852 = 1476×6741.

 

3,855

[Math.]  A regular polygon with this odd number (product of Fermat prime numbers) of sides is constructible by using only straightedge and compass. 3855 = 3×5×257.

 

3,860

[Geology]  The length (3860 miles = 6210.7 kilometers) of the Mississippi river.

 

3,861

[Math.]  38614 = 222,228,219,397,041.

 

3,864

[Math.]  18,095,112 = 6762×2676 = 4683×3864.

 

3,864 & 3,865

[Math.]  The pair (3864, 3865) is called Smith brothers (consecutive Smith numbers).