9999999 is nontrivially palindromic in base 10.
It is a trimorphic number since its cube, 999999700000029999999, ends in 9999999.
It is a nude number because it is divisible by every one of its digits.
It is an Ulam number.
9999999 is a nontrivial repdigit in base 10.
It is a plaindrome in base 10.
It is a nialpdrome in base 10.
It is a zygodrome in base 10.
It is a congruent number.
It is a Kaprekar number, because its square (99999980000001) can be partitioned into two parts whose sum is 9999999.
Almost surely, 29999999 is an apocalyptic number.
9999999 is a wasteful number, since it uses less digits than its factorization.
9999999 is an evil number, because the sum of its binary digits is even.
The square root of 9999999 is about 3162.2775020545. The cubic root of 9999999 is about 215.4434618217.
The spelling of 9999999 in words is "nine million, nine hundred ninety-nine thousand, nine hundred ninety-nine".