21581990 has 16 divisors (see below), whose sum is σ = 39795840. Its totient is φ = 8422080.

The previous prime is 21581969. The next prime is 21582013. The reversal of 21581990 is 9918512.

It is a self number, because there is not a number n which added to its sum of digits gives 21581990.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 25910 + ... + 26729.

It is an arithmetic number, because the mean of its divisors is an integer number (2487240).

Almost surely, 2^21581990 is an apocalyptic number.

21581990 is a deficient number, since it is larger than the sum of its proper divisors (18213850).

21581990 is a wasteful number, since it uses less digits than its factorization.

21581990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52687.

The product of its (nonzero) digits is 6480, while the sum is 35.

The square root of 21581990 is about 4645.6420438945. The cubic root of 21581990 is about 278.4179057025.

The spelling of 21581990 in words is "twenty-one million, five hundred eighty-one thousand, nine hundred ninety".