21229891 has 4 divisors (see below), whose sum is σ = 21577984. Its totient is φ = 20881800.

The previous prime is 21229883. The next prime is 21229919. The reversal of 21229891 is 19892212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21229891 - 2³ = 21229883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21227891) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 173955 + ... + 174076.

It is an arithmetic number, because the mean of its divisors is an integer number (5394496).

Almost surely, 2^21229891 is an apocalyptic number.

21229891 is a deficient number, since it is larger than the sum of its proper divisors (348093).

21229891 is an equidigital number, since it uses as much as digits as its factorization.

21229891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 348092.

The product of its digits is 5184, while the sum is 34.

The square root of 21229891 is about 4607.5905851106. The cubic root of 21229891 is about 276.8955150770.

It can be divided in two parts, 212 and 29891, that added together give a palindrome (30103).

The spelling of 21229891 in words is "twenty-one million, two hundred twenty-nine thousand, eight hundred ninety-one".