21491385 has 16 divisors (see below), whose sum is σ = 34473600. Its totient is φ = 11432960.

The previous prime is 21491381. The next prime is 21491411. The reversal of 21491385 is 58319412.

It is not a de Polignac number, because 21491385 - 2² = 21491381 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21491381) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5140 + ... + 8330.

It is an arithmetic number, because the mean of its divisors is an integer number (2154600).

Almost surely, 2^21491385 is an apocalyptic number.

It is an amenable number.

21491385 is a deficient number, since it is larger than the sum of its proper divisors (12982215).

21491385 is a wasteful number, since it uses less digits than its factorization.

21491385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3648.

The product of its digits is 8640, while the sum is 33.

The square root of 21491385 is about 4635.8801753281. The cubic root of 21491385 is about 278.0277433796.

The spelling of 21491385 in words is "twenty-one million, four hundred ninety-one thousand, three hundred eighty-five".