21143721 has 4 divisors (see below), whose sum is σ = 28191632. Its totient is φ = 14095812.

The previous prime is 21143719. The next prime is 21143723. The reversal of 21143721 is 12734112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21143719) and next prime (21143723).

It is not a de Polignac number, because 21143721 - 2¹ = 21143719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21143723) 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, 3523951 + ... + 3523956.

It is an arithmetic number, because the mean of its divisors is an integer number (7047908).

Almost surely, 2^21143721 is an apocalyptic number.

It is an amenable number.

21143721 is a deficient number, since it is larger than the sum of its proper divisors (7047911).

21143721 is an equidigital number, since it uses as much as digits as its factorization.

21143721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7047910.

The product of its digits is 336, while the sum is 21.

The square root of 21143721 is about 4598.2302030238. The cubic root of 21143721 is about 276.5203766864.

Adding to 21143721 its reverse (12734112), we get a palindrome (33877833).

The spelling of 21143721 in words is "twenty-one million, one hundred forty-three thousand, seven hundred twenty-one".