21186091 has 4 divisors (see below), whose sum is σ = 21340872. Its totient is φ = 21031312.

The previous prime is 21186079. The next prime is 21186103. The reversal of 21186091 is 19068112.

It is a happy number.

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

It is an interprime number because it is at equal distance from previous prime (21186079) and next prime (21186103).

It is a cyclic number.

It is not a de Polignac number, because 21186091 - 2¹⁵ = 21153323 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21186041) 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, 77185 + ... + 77458.

It is an arithmetic number, because the mean of its divisors is an integer number (5335218).

Almost surely, 2^21186091 is an apocalyptic number.

21186091 is a deficient number, since it is larger than the sum of its proper divisors (154781).

21186091 is a wasteful number, since it uses less digits than its factorization.

21186091 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154780.

The product of its (nonzero) digits is 864, while the sum is 28.

The square root of 21186091 is about 4602.8351045850. The cubic root of 21186091 is about 276.7049602646.

The spelling of 21186091 in words is "twenty-one million, one hundred eighty-six thousand, ninety-one".