20819521 has 2 divisors, whose sum is σ = 20819522. Its totient is φ = 20819520.

The previous prime is 20819467. The next prime is 20819563. The reversal of 20819521 is 12591802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 25921 = 4560^2 + 161^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20819521 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20819521.

It is not a weakly prime, because it can be changed into another prime (20819921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10409760 + 10409761.

It is an arithmetic number, because the mean of its divisors is an integer number (10409761).

Almost surely, 2^20819521 is an apocalyptic number.

It is an amenable number.

20819521 is a deficient number, since it is larger than the sum of its proper divisors (1).

20819521 is an equidigital number, since it uses as much as digits as its factorization.

20819521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 20819521 is about 4562.8413296980. The cubic root of 20819521 is about 275.0997808711.

The spelling of 20819521 in words is "twenty million, eight hundred nineteen thousand, five hundred twenty-one".