21391489 has 12 divisors (see below), whose sum is σ = 25356564. Its totient is φ = 17987424.

The previous prime is 21391481. The next prime is 21391523. The reversal of 21391489 is 98419312.

It can be written as a sum of positive squares in 2 ways, for example, as 14500864 + 6890625 = 3808^2 + 2625^2 .

It is not a de Polignac number, because 21391489 - 2³ = 21391481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21391481) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1522 + ... + 6715.

It is an arithmetic number, because the mean of its divisors is an integer number (2113047).

Almost surely, 2^21391489 is an apocalyptic number.

It is an amenable number.

21391489 is a deficient number, since it is larger than the sum of its proper divisors (3965075).

21391489 is an equidigital number, since it uses as much as digits as its factorization.

21391489 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8304 (or 8297 counting only the distinct ones).

The product of its digits is 15552, while the sum is 37.

The square root of 21391489 is about 4625.0934044622. The cubic root of 21391489 is about 277.5962991268.

The spelling of 21391489 in words is "twenty-one million, three hundred ninety-one thousand, four hundred eighty-nine".