21221791 has 2 divisors, whose sum is σ = 21221792. Its totient is φ = 21221790.

The previous prime is 21221779. The next prime is 21221821. The reversal of 21221791 is 19712212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21221791 - 2⁹ = 21221279 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610895 + 10610896.

It is an arithmetic number, because the mean of its divisors is an integer number (10610896).

Almost surely, 2^21221791 is an apocalyptic number.

21221791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221791 is an equidigital number, since it uses as much as digits as its factorization.

21221791 is an evil number, because the sum of its binary digits is even.

The product of its digits is 504, while the sum is 25.

The square root of 21221791 is about 4606.7115169066. The cubic root of 21221791 is about 276.8602952545.

The spelling of 21221791 in words is "twenty-one million, two hundred twenty-one thousand, seven hundred ninety-one".