21381890 has 8 divisors (see below), whose sum is σ = 38487420. Its totient is φ = 8552752.

The previous prime is 21381887. The next prime is 21381901. The reversal of 21381890 is 9818312.

It can be written as a sum of positive squares in 2 ways, for example, as 20529961 + 851929 = 4531^2 + 923^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1069085 + ... + 1069104.

Almost surely, 2^21381890 is an apocalyptic number.

21381890 is a deficient number, since it is larger than the sum of its proper divisors (17105530).

21381890 is a wasteful number, since it uses less digits than its factorization.

21381890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2138196.

The product of its (nonzero) digits is 3456, while the sum is 32.

The square root of 21381890 is about 4624.0555792508. The cubic root of 21381890 is about 277.5547709978.

The spelling of 21381890 in words is "twenty-one million, three hundred eighty-one thousand, eight hundred ninety".