21241991 has 2 divisors, whose sum is σ = 21241992. Its totient is φ = 21241990.

The previous prime is 21241973. The next prime is 21242047. The reversal of 21241991 is 19914212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21241991 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 (21241901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10620995 + 10620996.

It is an arithmetic number, because the mean of its divisors is an integer number (10620996).

Almost surely, 2^21241991 is an apocalyptic number.

21241991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21241991 is an equidigital number, since it uses as much as digits as its factorization.

21241991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1296, while the sum is 29.

The square root of 21241991 is about 4608.9034487609. The cubic root of 21241991 is about 276.9481107216.

The spelling of 21241991 in words is "twenty-one million, two hundred forty-one thousand, nine hundred ninety-one".