21294257 has 4 divisors (see below), whose sum is σ = 21305856. Its totient is φ = 21282660.

The previous prime is 21294253. The next prime is 21294263. The reversal of 21294257 is 75249212.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21294257 - 2² = 21294253 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21294253) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2369 + ... + 6942.

It is an arithmetic number, because the mean of its divisors is an integer number (5326464).

Almost surely, 2^21294257 is an apocalyptic number.

It is an amenable number.

21294257 is a deficient number, since it is larger than the sum of its proper divisors (11599).

21294257 is an equidigital number, since it uses as much as digits as its factorization.

21294257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11598.

The product of its digits is 10080, while the sum is 32.

The square root of 21294257 is about 4614.5700774828. The cubic root of 21294257 is about 277.1750686411.

It can be divided in two parts, 2129 and 4257, that multiplied together give a triangular number (9063153 = T₄₂₅₇).

The spelling of 21294257 in words is "twenty-one million, two hundred ninety-four thousand, two hundred fifty-seven".