It is an alternating number because its digits alternate between odd and even.
9090909090 is an undulating number in base 10.
It is an unprimeable number.
Almost surely, 29090909090 is an apocalyptic number.
9090909090 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 9090909090, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (12152439936).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
9090909090 is a wasteful number, since it uses less digits than its factorization.
9090909090 is an evil number, because the sum of its binary digits is even.
The square root of 9090909090 is about 95346.2589197919. The cubic root of 9090909090 is about 2087.0640223537.
9090909090 divided by its sum of digits (45) gives a palindrome (202020202).
Adding to 9090909090 its reverse (909090909), we get a palindrome (9999999999).
The spelling of 9090909090 in words is "nine billion, ninety million, nine hundred nine thousand, ninety".