21916991 has 2 divisors, whose sum is σ = 21916992. Its totient is φ = 21916990.

The previous prime is 21916981. The next prime is 21917003. The reversal of 21916991 is 19961912.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21916991 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21916901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10958495 + 10958496.

It is an arithmetic number, because the mean of its divisors is an integer number (10958496).

Almost surely, 2^21916991 is an apocalyptic number.

21916991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21916991 is an equidigital number, since it uses as much as digits as its factorization.

21916991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8748, while the sum is 38.

The square root of 21916991 is about 4681.5586079852. The cubic root of 21916991 is about 279.8510730133.

The spelling of 21916991 in words is "twenty-one million, nine hundred sixteen thousand, nine hundred ninety-one".