21865251 has 8 divisors (see below), whose sum is σ = 29176000. Its totient is φ = 14565672.

The previous prime is 21865243. The next prime is 21865279. The reversal of 21865251 is 15256812.

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

It is not a de Polignac number, because 21865251 - 2³ = 21865243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21865211) 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, 4500 + ... + 7998.

It is an arithmetic number, because the mean of its divisors is an integer number (3647000).

Almost surely, 2^21865251 is an apocalyptic number.

21865251 is a deficient number, since it is larger than the sum of its proper divisors (7310749).

21865251 is a wasteful number, since it uses less digits than its factorization.

21865251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5585.

The product of its digits is 4800, while the sum is 30.

The square root of 21865251 is about 4676.0294053823. The cubic root of 21865251 is about 279.6306823049.

The spelling of 21865251 in words is "twenty-one million, eight hundred sixty-five thousand, two hundred fifty-one".