90909090 has 96 divisors (see below), whose sum is σ = 243740016. Its totient is φ = 23500800.

The previous prime is 90909089. The next prime is 90909101. The reversal of 90909090 is 9090909.

It can be written as a sum of positive squares in 8 ways, for example, as 71115489 + 19793601 = 8433^2 + 4449^2 .

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is an alternating number because its digits alternate between odd and even.

90909090 is an undulating number in base 10.

90909090 is a modest number, since divided by 909090 gives 90 as remainder.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 663502 + ... + 663638.

Almost surely, 2^90909090 is an apocalyptic number.

90909090 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 90909090, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (121870008).

90909090 is an abundant number, since it is smaller than the sum of its proper divisors (152830926).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

90909090 is a wasteful number, since it uses less digits than its factorization.

90909090 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 324 (or 321 counting only the distinct ones).

The product of its (nonzero) digits is 6561, while the sum is 36.

The square root of 90909090 is about 9534.6258447828. The cubic root of 90909090 is about 449.6443115238.

Adding to 90909090 its reverse (9090909), we get a palindrome (99999999).

The spelling of 90909090 in words is "ninety million, nine hundred nine thousand, ninety".