19919821 has 2 divisors, whose sum is σ = 19919822. Its totient is φ = 19919820.

The previous prime is 19919819. The next prime is 19919827. The reversal of 19919821 is 12891991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 1550025 = 4286^2 + 1245^2 .

It is a cyclic number.

It is not a de Polignac number, because 19919821 - 2¹ = 19919819 is a prime.

Together with 19919819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19919827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9959910 + 9959911.

It is an arithmetic number, because the mean of its divisors is an integer number (9959911).

Almost surely, 2^19919821 is an apocalyptic number.

It is an amenable number.

19919821 is a deficient number, since it is larger than the sum of its proper divisors (1).

19919821 is an equidigital number, since it uses as much as digits as its factorization.

19919821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11664, while the sum is 40.

The square root of 19919821 is about 4463.1626678847. The cubic root of 19919821 is about 271.0785437019.

The spelling of 19919821 in words is "nineteen million, nine hundred nineteen thousand, eight hundred twenty-one".