21191831 has 2 divisors, whose sum is σ = 21191832. Its totient is φ = 21191830.

The previous prime is 21191813. The next prime is 21191857. The reversal of 21191831 is 13819112.

Together with previous prime (21191813) it forms an Ormiston pair, because they use the same digits, order apart.

It is an a-pointer prime, because the next prime (21191857) can be obtained adding 21191831 to its sum of digits (26).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21191831 - 2¹⁴ = 21175447 is a prime.

It is a super-2 number, since 2×21191831² = 898187402265122, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21191831.

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 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, 10595915 + 10595916.

It is an arithmetic number, because the mean of its divisors is an integer number (10595916).

Almost surely, 2^21191831 is an apocalyptic number.

21191831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21191831 is an equidigital number, since it uses as much as digits as its factorization.

21191831 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 432, while the sum is 26.

The square root of 21191831 is about 4603.4585911030. The cubic root of 21191831 is about 276.7299474610.

It can be divided in two parts, 21191 and 831, that added together give a palindrome (22022).

The spelling of 21191831 in words is "twenty-one million, one hundred ninety-one thousand, eight hundred thirty-one".