21523391 has 2 divisors, whose sum is σ = 21523392. Its totient is φ = 21523390.

The previous prime is 21523387. The next prime is 21523399. The reversal of 21523391 is 19332512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21523391 - 2² = 21523387 is a prime.

It is equal to p_1360961 and since 21523391 and 1360961 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 9.

It is a self number, because there is not a number n which added to its sum of digits gives 21523391.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21523399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761695 + 10761696.

It is an arithmetic number, because the mean of its divisors is an integer number (10761696).

Almost surely, 2^21523391 is an apocalyptic number.

21523391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523391 is an equidigital number, since it uses as much as digits as its factorization.

21523391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1620, while the sum is 26.

The square root of 21523391 is about 4639.3308784781. The cubic root of 21523391 is about 278.1656923333.

The spelling of 21523391 in words is "twenty-one million, five hundred twenty-three thousand, three hundred ninety-one".