21135257 has 8 divisors (see below), whose sum is σ = 24830400. Its totient is φ = 17735760.

The previous prime is 21135227. The next prime is 21135259. The reversal of 21135257 is 75253112.

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 21135257 - 2⁸ = 21135001 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21135259) 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, 73757 + ... + 74042.

It is an arithmetic number, because the mean of its divisors is an integer number (3103800).

Almost surely, 2^21135257 is an apocalyptic number.

It is an amenable number.

21135257 is a deficient number, since it is larger than the sum of its proper divisors (3695143).

21135257 is a wasteful number, since it uses less digits than its factorization.

21135257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 147823.

The product of its digits is 2100, while the sum is 26.

The square root of 21135257 is about 4597.3097568034. The cubic root of 21135257 is about 276.4834739918.

Adding to 21135257 its reverse (75253112), we get a palindrome (96388369).

The spelling of 21135257 in words is "twenty-one million, one hundred thirty-five thousand, two hundred fifty-seven".