21001990 has 32 divisors (see below), whose sum is σ = 39813120. Its totient is φ = 7961184.

The previous prime is 21001979. The next prime is 21001991. The reversal of 21001990 is 9910012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001991) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28851 + ... + 29569.

It is an arithmetic number, because the mean of its divisors is an integer number (1244160).

Almost surely, 2^21001990 is an apocalyptic number.

21001990 is a deficient number, since it is larger than the sum of its proper divisors (18811130).

21001990 is a wasteful number, since it uses less digits than its factorization.

21001990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 876.

The product of its (nonzero) digits is 162, while the sum is 22.

The square root of 21001990 is about 4582.7928166130. The cubic root of 21001990 is about 275.9011320599.

The spelling of 21001990 in words is "twenty-one million, one thousand, nine hundred ninety".