21396691 has 2 divisors, whose sum is σ = 21396692. Its totient is φ = 21396690.

The previous prime is 21396673. The next prime is 21396701. The reversal of 21396691 is 19669312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21396691 - 2¹⁷ = 21265619 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21396691.

It is not a weakly prime, because it can be changed into another prime (21396611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698345 + 10698346.

It is an arithmetic number, because the mean of its divisors is an integer number (10698346).

Almost surely, 2^21396691 is an apocalyptic number.

21396691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21396691 is an equidigital number, since it uses as much as digits as its factorization.

21396691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 17496, while the sum is 37.

The square root of 21396691 is about 4625.6557372982. The cubic root of 21396691 is about 277.6187993356.

The spelling of 21396691 in words is "twenty-one million, three hundred ninety-six thousand, six hundred ninety-one".