21621191 has 4 divisors (see below), whose sum is σ = 22029192. Its totient is φ = 21213192.

The previous prime is 21621181. The next prime is 21621233. The reversal of 21621191 is 19112612.

It is a happy number.

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 21621191 - 2¹⁸ = 21359047 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621121) 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, 203921 + ... + 204026.

It is an arithmetic number, because the mean of its divisors is an integer number (5507298).

Almost surely, 2^21621191 is an apocalyptic number.

21621191 is a deficient number, since it is larger than the sum of its proper divisors (408001).

21621191 is an equidigital number, since it uses as much as digits as its factorization.

21621191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408000.

The product of its digits is 216, while the sum is 23.

The square root of 21621191 is about 4649.8592451815. The cubic root of 21621191 is about 278.5863742396.

It can be divided in two parts, 21621 and 191, that added together give a palindrome (21812).

The spelling of 21621191 in words is "twenty-one million, six hundred twenty-one thousand, one hundred ninety-one".