It is a congruent number.
21806558 is an apocalyptic number.
It is a practical number, because each smaller number is the sum of distinct divisors of 1806558, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2177280).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
1806558 is a wasteful number, since it uses less digits than its factorization.
1806558 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 113.
The square root of 1806558 is about 1344.0825867483. The cubic root of 1806558 is about 121.7915907924.
The spelling of 1806558 in words is "one million, eight hundred six thousand, five hundred fifty-eight".