21047251 has 4 divisors (see below), whose sum is σ = 21060000. Its totient is φ = 21034504.

The previous prime is 21047237. The next prime is 21047281. The reversal of 21047251 is 15274012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21047251 - 2²³ = 12658643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21047281) 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, 3451 + ... + 7348.

It is an arithmetic number, because the mean of its divisors is an integer number (5265000).

Almost surely, 2^21047251 is an apocalyptic number.

21047251 is a deficient number, since it is larger than the sum of its proper divisors (12749).

21047251 is a wasteful number, since it uses less digits than its factorization.

21047251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12748.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21047251 is about 4587.7283049457. The cubic root of 21047251 is about 276.0991863282.

The spelling of 21047251 in words is "twenty-one million, forty-seven thousand, two hundred fifty-one".