21373991 has 2 divisors, whose sum is σ = 21373992. Its totient is φ = 21373990.

The previous prime is 21373987. The next prime is 21374011. The reversal of 21373991 is 19937312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21373991 - 2² = 21373987 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 (21373591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10686995 + 10686996.

It is an arithmetic number, because the mean of its divisors is an integer number (10686996).

Almost surely, 2^21373991 is an apocalyptic number.

21373991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21373991 is an equidigital number, since it uses as much as digits as its factorization.

21373991 is an evil number, because the sum of its binary digits is even.

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

The square root of 21373991 is about 4623.2013799963. The cubic root of 21373991 is about 277.5205882514.

The spelling of 21373991 in words is "twenty-one million, three hundred seventy-three thousand, nine hundred ninety-one".