21219931 has 4 divisors (see below), whose sum is σ = 21407832. Its totient is φ = 21032032.

The previous prime is 21219929. The next prime is 21219937. The reversal of 21219931 is 13991212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21219931 - 2¹ = 21219929 is a prime.

It is a super-2 number, since 2×21219931² = 900570943289522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21219931.

It is not an unprimeable number, because it can be changed into a prime (21219937) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 93781 + ... + 94006.

It is an arithmetic number, because the mean of its divisors is an integer number (5351958).

Almost surely, 2^21219931 is an apocalyptic number.

21219931 is a deficient number, since it is larger than the sum of its proper divisors (187901).

21219931 is a wasteful number, since it uses less digits than its factorization.

21219931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 187900.

The product of its digits is 972, while the sum is 28.

The square root of 21219931 is about 4606.5096331170. The cubic root of 21219931 is about 276.8522064745.

The spelling of 21219931 in words is "twenty-one million, two hundred nineteen thousand, nine hundred thirty-one".