21337991 has 4 divisors (see below), whose sum is σ = 21431400. Its totient is φ = 21244584.

The previous prime is 21337957. The next prime is 21338003. The reversal of 21337991 is 19973312.

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-21337991 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 (21337891) 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, 46361 + ... + 46818.

It is an arithmetic number, because the mean of its divisors is an integer number (5357850).

Almost surely, 2^21337991 is an apocalyptic number.

21337991 is a deficient number, since it is larger than the sum of its proper divisors (93409).

21337991 is an equidigital number, since it uses as much as digits as its factorization.

21337991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 93408.

The product of its digits is 10206, while the sum is 35.

The square root of 21337991 is about 4619.3063332063. The cubic root of 21337991 is about 277.3646923071.

The spelling of 21337991 in words is "twenty-one million, three hundred thirty-seven thousand, nine hundred ninety-one".