21517491 has 4 divisors (see below), whose sum is σ = 28689992. Its totient is φ = 14344992.

The previous prime is 21517471. The next prime is 21517499. The reversal of 21517491 is 19471512.

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

It is not a de Polignac number, because 21517491 - 2⁵ = 21517459 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21517499) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3586246 + ... + 3586251.

It is an arithmetic number, because the mean of its divisors is an integer number (7172498).

Almost surely, 2^21517491 is an apocalyptic number.

21517491 is a deficient number, since it is larger than the sum of its proper divisors (7172501).

21517491 is an equidigital number, since it uses as much as digits as its factorization.

21517491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7172500.

The product of its digits is 2520, while the sum is 30.

The square root of 21517491 is about 4638.6949673373. The cubic root of 21517491 is about 278.1402730493.

The spelling of 21517491 in words is "twenty-one million, five hundred seventeen thousand, four hundred ninety-one".