21393521 has 2 divisors, whose sum is σ = 21393522. Its totient is φ = 21393520.

The previous prime is 21393481. The next prime is 21393551. The reversal of 21393521 is 12539312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11999296 + 9394225 = 3464^2 + 3065^2 .

It is a cyclic number.

It is not a de Polignac number, because 21393521 - 2⁶ = 21393457 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21393551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10696760 + 10696761.

It is an arithmetic number, because the mean of its divisors is an integer number (10696761).

Almost surely, 2^21393521 is an apocalyptic number.

It is an amenable number.

21393521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21393521 is an equidigital number, since it uses as much as digits as its factorization.

21393521 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 21393521 is about 4625.3130704851. The cubic root of 21393521 is about 277.6050885698.

The spelling of 21393521 in words is "twenty-one million, three hundred ninety-three thousand, five hundred twenty-one".