21781489 has 4 divisors (see below), whose sum is σ = 21816640. Its totient is φ = 21746340.

The previous prime is 21781481. The next prime is 21781511. The reversal of 21781489 is 98418712.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 21781489 - 2³ = 21781481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21781481) 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, 16629 + ... + 17890.

It is an arithmetic number, because the mean of its divisors is an integer number (5454160).

Almost surely, 2^21781489 is an apocalyptic number.

It is an amenable number.

21781489 is a deficient number, since it is larger than the sum of its proper divisors (35151).

21781489 is an equidigital number, since it uses as much as digits as its factorization.

21781489 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35150.

The product of its digits is 32256, while the sum is 40.

The square root of 21781489 is about 4667.0642806801. The cubic root of 21781489 is about 279.2731530893.

The spelling of 21781489 in words is "twenty-one million, seven hundred eighty-one thousand, four hundred eighty-nine".