21221751 has 4 divisors (see below), whose sum is σ = 28295672. Its totient is φ = 14147832.

The previous prime is 21221749. The next prime is 21221773. The reversal of 21221751 is 15712212.

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

It is not a de Polignac number, because 21221751 - 2¹ = 21221749 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 (21221731) 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, 3536956 + ... + 3536961.

It is an arithmetic number, because the mean of its divisors is an integer number (7073918).

Almost surely, 2^21221751 is an apocalyptic number.

21221751 is a deficient number, since it is larger than the sum of its proper divisors (7073921).

21221751 is an equidigital number, since it uses as much as digits as its factorization.

21221751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7073920.

The product of its digits is 280, while the sum is 21.

The square root of 21221751 is about 4606.7071754128. The cubic root of 21221751 is about 276.8601213072.

Adding to 21221751 its reverse (15712212), we get a palindrome (36933963).

The spelling of 21221751 in words is "twenty-one million, two hundred twenty-one thousand, seven hundred fifty-one".