21723931 has 2 divisors, whose sum is σ = 21723932. Its totient is φ = 21723930.

The previous prime is 21723913. The next prime is 21723959. The reversal of 21723931 is 13932712.

Together with previous prime (21723913) it forms an Ormiston pair, because they use the same digits, order apart.

It is an a-pointer prime, because the next prime (21723959) can be obtained adding 21723931 to its sum of digits (28).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21723931 - 2⁹ = 21723419 is a prime.

It is a super-2 number, since 2×21723931² = 943858356185522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21723931.

It is not a weakly prime, because it can be changed into another prime (21723971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10861965 + 10861966.

It is an arithmetic number, because the mean of its divisors is an integer number (10861966).

Almost surely, 2^21723931 is an apocalyptic number.

21723931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21723931 is an equidigital number, since it uses as much as digits as its factorization.

21723931 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2268, while the sum is 28.

The square root of 21723931 is about 4660.8937984039. The cubic root of 21723931 is about 279.0269412112.

The spelling of 21723931 in words is "twenty-one million, seven hundred twenty-three thousand, nine hundred thirty-one".