21091487 has 4 divisors (see below), whose sum is σ = 21328560. Its totient is φ = 20854416.

The previous prime is 21091481. The next prime is 21091489. The reversal of 21091487 is 78419012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21091487 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21091481) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 118403 + ... + 118580.

It is an arithmetic number, because the mean of its divisors is an integer number (5332140).

Almost surely, 2^21091487 is an apocalyptic number.

21091487 is a deficient number, since it is larger than the sum of its proper divisors (237073).

21091487 is an equidigital number, since it uses as much as digits as its factorization.

21091487 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 237072.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21091487 is about 4592.5468968754. The cubic root of 21091487 is about 276.2924811993.

The spelling of 21091487 in words is "twenty-one million, ninety-one thousand, four hundred eighty-seven".