21258691 has 2 divisors, whose sum is σ = 21258692. Its totient is φ = 21258690.

The previous prime is 21258689. The next prime is 21258733. The reversal of 21258691 is 19685212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21258691 - 2¹ = 21258689 is a prime.

Together with 21258689, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21258661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10629345 + 10629346.

It is an arithmetic number, because the mean of its divisors is an integer number (10629346).

Almost surely, 2^21258691 is an apocalyptic number.

21258691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21258691 is an equidigital number, since it uses as much as digits as its factorization.

21258691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 34.

The square root of 21258691 is about 4610.7148035852. The cubic root of 21258691 is about 277.0206686085.

It can be divided in two parts, 2125 and 8691, that added together give a square (10816 = 104²).

The spelling of 21258691 in words is "twenty-one million, two hundred fifty-eight thousand, six hundred ninety-one".