21520990 has 16 divisors (see below), whose sum is σ = 38815920. Its totient is φ = 8591040.

The previous prime is 21520949. The next prime is 21520999. The reversal of 21520990 is 9902512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520999) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 3826 + ... + 7594.

It is an arithmetic number, because the mean of its divisors is an integer number (2425995).

Almost surely, 2^21520990 is an apocalyptic number.

21520990 is a deficient number, since it is larger than the sum of its proper divisors (17294930).

21520990 is a wasteful number, since it uses less digits than its factorization.

21520990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4347.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 21520990 is about 4639.0721054970. The cubic root of 21520990 is about 278.1553485378.

The spelling of 21520990 in words is "twenty-one million, five hundred twenty thousand, nine hundred ninety".