21191591 has 2 divisors, whose sum is σ = 21191592. Its totient is φ = 21191590.

The previous prime is 21191581. The next prime is 21191603. The reversal of 21191591 is 19519112.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21191591 is a prime.

It is a super-2 number, since 2×21191591² = 898167058222562, which contains 22 as substring.

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 (21191531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10595795 + 10595796.

It is an arithmetic number, because the mean of its divisors is an integer number (10595796).

Almost surely, 2^21191591 is an apocalyptic number.

21191591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21191591 is an equidigital number, since it uses as much as digits as its factorization.

21191591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 810, while the sum is 29.

The square root of 21191591 is about 4603.4325236719. The cubic root of 21191591 is about 276.7289027906.

The spelling of 21191591 in words is "twenty-one million, one hundred ninety-one thousand, five hundred ninety-one".