21090099 has 4 divisors (see below), whose sum is σ = 28120136. Its totient is φ = 14060064.

The previous prime is 21090073. The next prime is 21090101. The reversal of 21090099 is 99009012.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21090099 - 2⁵ = 21090067 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21090299) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 3515014 + ... + 3515019.

It is an arithmetic number, because the mean of its divisors is an integer number (7030034).

Almost surely, 2^21090099 is an apocalyptic number.

21090099 is a deficient number, since it is larger than the sum of its proper divisors (7030037).

21090099 is an equidigital number, since it uses as much as digits as its factorization.

21090099 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7030036.

The product of its (nonzero) digits is 1458, while the sum is 30.

The square root of 21090099 is about 4592.3957799824. The cubic root of 21090099 is about 276.2864202646.

It can be divided in two parts, 210 and 90099, that added together give a palindrome (90309).

The spelling of 21090099 in words is "twenty-one million, ninety thousand, ninety-nine".