It is a nialpdrome in base 10.
It is a zygodrome in base 10.
It is a congruent number.
It is an unprimeable number.
Almost surely, 299999966 is an apocalyptic number.
It is a practical number, because each smaller number is the sum of distinct divisors of 99999966, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (110669832).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
99999966 is a wasteful number, since it uses less digits than its factorization.
99999966 is an odious number, because the sum of its binary digits is odd.
The square root of 99999966 is about 9999.9982999999. The cubic root of 99999966 is about 464.1588307566.
99999966 divided by its sum of digits (66) gives a palindrome (1515151).
The spelling of 99999966 in words is "ninety-nine million, nine hundred ninety-nine thousand, nine hundred sixty-six".