21278989 has 8 divisors (see below), whose sum is σ = 22268672. Its totient is φ = 20308320.

The previous prime is 21278981. The next prime is 21279029. The reversal of 21278989 is 98987212.

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 21278989 - 2³ = 21278981 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21278981) 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, 2439 + ... + 6964.

It is an arithmetic number, because the mean of its divisors is an integer number (2783584).

Almost surely, 2^21278989 is an apocalyptic number.

It is an amenable number.

21278989 is a deficient number, since it is larger than the sum of its proper divisors (989683).

21278989 is an equidigital number, since it uses as much as digits as its factorization.

21278989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9507.

The product of its digits is 145152, while the sum is 46.

The square root of 21278989 is about 4612.9154555444. The cubic root of 21278989 is about 277.1088078839.

It can be divided in two parts, 212789 and 89, that added together give a triangular number (212878 = T₆₅₂).

The spelling of 21278989 in words is "twenty-one million, two hundred seventy-eight thousand, nine hundred eighty-nine".