21021823 has 2 divisors, whose sum is σ = 21021824. Its totient is φ = 21021822.

The previous prime is 21021799. The next prime is 21021827. The reversal of 21021823 is 32812012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21021823 - 2¹³ = 21013631 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21021823.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21021827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510911 + 10510912.

It is an arithmetic number, because the mean of its divisors is an integer number (10510912).

Almost surely, 2^21021823 is an apocalyptic number.

21021823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021823 is an equidigital number, since it uses as much as digits as its factorization.

21021823 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21021823 is about 4584.9561611863. The cubic root of 21021823 is about 275.9879528103.

Adding to 21021823 its reverse (32812012), we get a palindrome (53833835).

The spelling of 21021823 in words is "twenty-one million, twenty-one thousand, eight hundred twenty-three".