21438251 has 8 divisors (see below), whose sum is σ = 23047680. Its totient is φ = 19876968.

The previous prime is 21438239. The next prime is 21438253. The reversal of 21438251 is 15283412.

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 21438251 - 2⁶ = 21438187 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21438251.

It is not an unprimeable number, because it can be changed into a prime (21438253) 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, 11111 + ... + 12896.

It is an arithmetic number, because the mean of its divisors is an integer number (2880960).

Almost surely, 2^21438251 is an apocalyptic number.

21438251 is a deficient number, since it is larger than the sum of its proper divisors (1609429).

21438251 is a wasteful number, since it uses less digits than its factorization.

21438251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24073.

The product of its digits is 1920, while the sum is 26.

The square root of 21438251 is about 4630.1458940297. The cubic root of 21438251 is about 277.7984279700.

The spelling of 21438251 in words is "twenty-one million, four hundred thirty-eight thousand, two hundred fifty-one".