21395257 has 8 divisors (see below), whose sum is σ = 23140040. Its totient is φ = 19664640.

The previous prime is 21395251. The next prime is 21395261. The reversal of 21395257 is 75259312.

It can be written as a sum of positive squares in 4 ways, for example, as 2524921 + 18870336 = 1589^2 + 4344^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21395257 - 2³ = 21395249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21395251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 282 + ... + 6547.

It is an arithmetic number, because the mean of its divisors is an integer number (2892505).

Almost surely, 2^21395257 is an apocalyptic number.

It is an amenable number.

21395257 is a deficient number, since it is larger than the sum of its proper divisors (1744783).

21395257 is a wasteful number, since it uses less digits than its factorization.

21395257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7083.

The product of its digits is 18900, while the sum is 34.

The square root of 21395257 is about 4625.5007296508. The cubic root of 21395257 is about 277.6125972200.

It can be divided in two parts, 2139 and 5257, that added together give a square (7396 = 86²).

The spelling of 21395257 in words is "twenty-one million, three hundred ninety-five thousand, two hundred fifty-seven".