21681790 has 16 divisors (see below), whose sum is σ = 42029568. Its totient is φ = 8005536.

The previous prime is 21681769. The next prime is 21681797. The reversal of 21681790 is 9718612.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681797) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 83262 + ... + 83521.

It is an arithmetic number, because the mean of its divisors is an integer number (2626848).

Almost surely, 2^21681790 is an apocalyptic number.

21681790 is a deficient number, since it is larger than the sum of its proper divisors (20347778).

21681790 is a wasteful number, since it uses less digits than its factorization.

21681790 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166803.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 21681790 is about 4656.3709044706. The cubic root of 21681790 is about 278.8464016681.

The spelling of 21681790 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred ninety".