21186491 has 4 divisors (see below), whose sum is σ = 21267312. Its totient is φ = 21105672.

The previous prime is 21186469. The next prime is 21186493. The reversal of 21186491 is 19468112.

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-21186491 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21186493) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40016 + ... + 40541.

It is an arithmetic number, because the mean of its divisors is an integer number (5316828).

Almost surely, 2^21186491 is an apocalyptic number.

21186491 is a deficient number, since it is larger than the sum of its proper divisors (80821).

21186491 is an equidigital number, since it uses as much as digits as its factorization.

21186491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80820.

The product of its digits is 3456, while the sum is 32.

The square root of 21186491 is about 4602.8785558605. The cubic root of 21186491 is about 276.7067016789.

The spelling of 21186491 in words is "twenty-one million, one hundred eighty-six thousand, four hundred ninety-one".