21388723 has 2 divisors, whose sum is σ = 21388724. Its totient is φ = 21388722.

The previous prime is 21388721. The next prime is 21388751. The reversal of 21388723 is 32788312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21388723 - 2¹ = 21388721 is a prime.

Together with 21388721, it forms a pair of twin primes.

It is equal to p_1352986 and since 21388723 and 1352986 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21388721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10694361 + 10694362.

It is an arithmetic number, because the mean of its divisors is an integer number (10694362).

Almost surely, 2^21388723 is an apocalyptic number.

21388723 is a deficient number, since it is larger than the sum of its proper divisors (1).

21388723 is an equidigital number, since it uses as much as digits as its factorization.

21388723 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16128, while the sum is 34.

The square root of 21388723 is about 4624.7943738073. The cubic root of 21388723 is about 277.5843338625.

The spelling of 21388723 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred twenty-three".