19717921 has 2 divisors, whose sum is σ = 19717922. Its totient is φ = 19717920.

The previous prime is 19717913. The next prime is 19717931. The reversal of 19717921 is 12971791.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18190225 + 1527696 = 4265^2 + 1236^2 .

It is a cyclic number.

It is not a de Polignac number, because 19717921 - 2³ = 19717913 is a prime.

It is not a weakly prime, because it can be changed into another prime (19717931) 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, 9858960 + 9858961.

It is an arithmetic number, because the mean of its divisors is an integer number (9858961).

Almost surely, 2^19717921 is an apocalyptic number.

It is an amenable number.

19717921 is a deficient number, since it is larger than the sum of its proper divisors (1).

19717921 is an equidigital number, since it uses as much as digits as its factorization.

19717921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7938, while the sum is 37.

The square root of 19717921 is about 4440.4865724378. The cubic root of 19717921 is about 270.1595810169.

The spelling of 19717921 in words is "nineteen million, seven hundred seventeen thousand, nine hundred twenty-one".