21023591 has 2 divisors, whose sum is σ = 21023592. Its totient is φ = 21023590.

The previous prime is 21023573. The next prime is 21023599. The reversal of 21023591 is 19532012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21023591 - 2²² = 16829287 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is equal to p_1331384 and since 21023591 and 1331384 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21023599) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10511795 + 10511796.

It is an arithmetic number, because the mean of its divisors is an integer number (10511796).

Almost surely, 2^21023591 is an apocalyptic number.

21023591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21023591 is an equidigital number, since it uses as much as digits as its factorization.

21023591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21023591 is about 4585.1489615933. The cubic root of 21023591 is about 275.9956897388.

The spelling of 21023591 in words is "twenty-one million, twenty-three thousand, five hundred ninety-one".