21007891 has 2 divisors, whose sum is σ = 21007892. Its totient is φ = 21007890.

The previous prime is 21007879. The next prime is 21007913. The reversal of 21007891 is 19870012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21007891 - 2²³ = 12619283 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21007871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503945 + 10503946.

It is an arithmetic number, because the mean of its divisors is an integer number (10503946).

Almost surely, 2^21007891 is an apocalyptic number.

21007891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21007891 is an equidigital number, since it uses as much as digits as its factorization.

21007891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 21007891 is about 4583.4365927762. The cubic root of 21007891 is about 275.9269699308.

The spelling of 21007891 in words is "twenty-one million, seven thousand, eight hundred ninety-one".