21319931 has 4 divisors (see below), whose sum is σ = 21428352. Its totient is φ = 21211512.

The previous prime is 21319889. The next prime is 21319937. The reversal of 21319931 is 13991312.

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 21319931 - 2¹⁸ = 21057787 is a prime.

It is a super-2 number, since 2×21319931² = 909078915689522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21319894 and 21319903.

It is not an unprimeable number, because it can be changed into a prime (21319937) 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, 53915 + ... + 54308.

It is an arithmetic number, because the mean of its divisors is an integer number (5357088).

Almost surely, 2^21319931 is an apocalyptic number.

21319931 is a deficient number, since it is larger than the sum of its proper divisors (108421).

21319931 is a wasteful number, since it uses less digits than its factorization.

21319931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108420.

The product of its digits is 1458, while the sum is 29.

The square root of 21319931 is about 4617.3510804356. The cubic root of 21319931 is about 277.2864184553.

The spelling of 21319931 in words is "twenty-one million, three hundred nineteen thousand, nine hundred thirty-one".