19910921 has 8 divisors (see below), whose sum is σ = 20640840. Its totient is φ = 19191168.

The previous prime is 19910903. The next prime is 19910951. The reversal of 19910921 is 12901991.

It can be written as a sum of positive squares in 4 ways, for example, as 8042896 + 11868025 = 2836^2 + 3445^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 19910921 - 2⁶ = 19910857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19910951) 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, 1565 + ... + 6501.

It is an arithmetic number, because the mean of its divisors is an integer number (2580105).

Almost surely, 2^19910921 is an apocalyptic number.

It is an amenable number.

19910921 is a deficient number, since it is larger than the sum of its proper divisors (729919).

19910921 is a wasteful number, since it uses less digits than its factorization.

19910921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5083.

The product of its (nonzero) digits is 1458, while the sum is 32.

The square root of 19910921 is about 4462.1655056710. The cubic root of 19910921 is about 271.0381658551.

The spelling of 19910921 in words is "nineteen million, nine hundred ten thousand, nine hundred twenty-one".