21721641 has 8 divisors (see below), whose sum is σ = 28995744. Its totient is φ = 14464320.

The previous prime is 21721621. The next prime is 21721717. The reversal of 21721641 is 14612712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21721641 - 2⁶ = 21721577 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21721621) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 775 + ... + 6636.

It is an arithmetic number, because the mean of its divisors is an integer number (3624468).

Almost surely, 2^21721641 is an apocalyptic number.

It is an amenable number.

21721641 is a deficient number, since it is larger than the sum of its proper divisors (7274103).

21721641 is an equidigital number, since it uses as much as digits as its factorization.

21721641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8391.

The product of its digits is 672, while the sum is 24.

The square root of 21721641 is about 4660.6481308934. The cubic root of 21721641 is about 279.0171364457.

The spelling of 21721641 in words is "twenty-one million, seven hundred twenty-one thousand, six hundred forty-one".