21258709 has 4 divisors (see below), whose sum is σ = 21272416. Its totient is φ = 21245004.

The previous prime is 21258691. The next prime is 21258733. The reversal of 21258709 is 90785212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21258709 - 2¹¹ = 21256661 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21258779) 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 in 3 ways as a sum of consecutive naturals, for example, 4179 + ... + 7744.

It is an arithmetic number, because the mean of its divisors is an integer number (5318104).

Almost surely, 2^21258709 is an apocalyptic number.

It is an amenable number.

21258709 is a deficient number, since it is larger than the sum of its proper divisors (13707).

21258709 is a wasteful number, since it uses less digits than its factorization.

21258709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13706.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21258709 is about 4610.7167555598. The cubic root of 21258709 is about 277.0207467941.

The spelling of 21258709 in words is "twenty-one million, two hundred fifty-eight thousand, seven hundred nine".