999990 divided by its sum of digits (45) gives a palindrome (22222).
999990 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a nialpdrome in base 10.
It is a congruent number.
It is an unprimeable number.
999990 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
2999990 is an apocalyptic number.
999990 is a gapful number since it is divisible by the number (90) formed by its first and last digit.
It is a practical number, because each smaller number is the sum of distinct divisors of 999990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1336608).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
999990 is a wasteful number, since it uses less digits than its factorization.
999990 is an evil number, because the sum of its binary digits is even.
The square root of 999990 is about 999.9949999875. The cubic root of 999990 is about 99.9996666656. Note that the first 3 decimals are identical.
The spelling of 999990 in words is "nine hundred ninety-nine thousand, nine hundred ninety".