21210691 has 2 divisors, whose sum is σ = 21210692. Its totient is φ = 21210690.

The previous prime is 21210649. The next prime is 21210697. The reversal of 21210691 is 19601212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21210691 - 2⁹ = 21210179 is a prime.

It is not a weakly prime, because it can be changed into another prime (21210697) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605345 + 10605346.

It is an arithmetic number, because the mean of its divisors is an integer number (10605346).

Almost surely, 2^21210691 is an apocalyptic number.

21210691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210691 is an equidigital number, since it uses as much as digits as its factorization.

21210691 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21210691 is about 4605.5065953704. The cubic root of 21210691 is about 276.8120164950.

The spelling of 21210691 in words is "twenty-one million, two hundred ten thousand, six hundred ninety-one".