21489751 has 24 divisors (see below), whose sum is σ = 24668064. Its totient is φ = 18670080.

The previous prime is 21489739. The next prime is 21489761. The reversal of 21489751 is 15798412.

It is not a de Polignac number, because 21489751 - 2⁵ = 21489719 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 21489751.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21489701) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 352261 + ... + 352321.

It is an arithmetic number, because the mean of its divisors is an integer number (1027836).

Almost surely, 2^21489751 is an apocalyptic number.

21489751 is a deficient number, since it is larger than the sum of its proper divisors (3178313).

21489751 is a wasteful number, since it uses less digits than its factorization.

21489751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 171 (or 154 counting only the distinct ones).

The product of its digits is 20160, while the sum is 37.

The square root of 21489751 is about 4635.7039379149. The cubic root of 21489751 is about 278.0206970082.

The spelling of 21489751 in words is "twenty-one million, four hundred eighty-nine thousand, seven hundred fifty-one".