21012491 has 4 divisors (see below), whose sum is σ = 21163800. Its totient is φ = 20861184.

The previous prime is 21012457. The next prime is 21012503. The reversal of 21012491 is 19421012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21012491 - 2²² = 16818187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21012401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 75446 + ... + 75723.

It is an arithmetic number, because the mean of its divisors is an integer number (5290950).

Almost surely, 2^21012491 is an apocalyptic number.

21012491 is a deficient number, since it is larger than the sum of its proper divisors (151309).

21012491 is a wasteful number, since it uses less digits than its factorization.

21012491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 151308.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 21012491 is about 4583.9383721861. The cubic root of 21012491 is about 275.9471079420.

The spelling of 21012491 in words is "twenty-one million, twelve thousand, four hundred ninety-one".