30991921 has 2 divisors, whose sum is σ = 30991922. Its totient is φ = 30991920.

The previous prime is 30991913. The next prime is 30991927. The reversal of 30991921 is 12919903.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17338896 + 13653025 = 4164^2 + 3695^2 .

It is an emirp because it is prime and its reverse (12919903) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 30991921 - 2³ = 30991913 is a prime.

It is not a weakly prime, because it can be changed into another prime (30991927) 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, 15495960 + 15495961.

It is an arithmetic number, because the mean of its divisors is an integer number (15495961).

Almost surely, 2^30991921 is an apocalyptic number.

It is an amenable number.

30991921 is a deficient number, since it is larger than the sum of its proper divisors (1).

30991921 is an equidigital number, since it uses as much as digits as its factorization.

30991921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 30991921 is about 5567.0387999366. The cubic root of 30991921 is about 314.1107733904.

The spelling of 30991921 in words is "thirty million, nine hundred ninety-one thousand, nine hundred twenty-one".