21123990 has 48 divisors (see below), whose sum is σ = 56963088. Its totient is φ = 5632416.

The previous prime is 21123983. The next prime is 21124001. The reversal of 21123990 is 9932112.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1917 + ... + 6776.

It is an arithmetic number, because the mean of its divisors is an integer number (1186731).

Almost surely, 2^21123990 is an apocalyptic number.

21123990 is an abundant number, since it is smaller than the sum of its proper divisors (35839098).

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

21123990 is an equidigital number, since it uses as much as digits as its factorization.

21123990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8715 (or 8703 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21123990 is about 4596.0842028840. The cubic root of 21123990 is about 276.4343350417.

The spelling of 21123990 in words is "twenty-one million, one hundred twenty-three thousand, nine hundred ninety".