21292391 has 2 divisors, whose sum is σ = 21292392. Its totient is φ = 21292390.

The previous prime is 21292367. The next prime is 21292393. The reversal of 21292391 is 19329212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21292391 - 2¹⁰ = 21291367 is a prime.

It is a Sophie Germain prime.

Together with 21292393, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21292393) 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 as a sum of consecutive naturals, namely, 10646195 + 10646196.

It is an arithmetic number, because the mean of its divisors is an integer number (10646196).

Almost surely, 2^21292391 is an apocalyptic number.

21292391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21292391 is an equidigital number, since it uses as much as digits as its factorization.

21292391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 29.

The square root of 21292391 is about 4614.3678873709. The cubic root of 21292391 is about 277.1669721892.

The spelling of 21292391 in words is "twenty-one million, two hundred ninety-two thousand, three hundred ninety-one".