21329661 has 4 divisors (see below), whose sum is σ = 28439552. Its totient is φ = 14219772.

The previous prime is 21329641. The next prime is 21329663. The reversal of 21329661 is 16692312.

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 not a de Polignac number, because 21329661 - 2⁵ = 21329629 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 (21329663) 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, 3554941 + ... + 3554946.

It is an arithmetic number, because the mean of its divisors is an integer number (7109888).

Almost surely, 2^21329661 is an apocalyptic number.

It is an amenable number.

21329661 is a deficient number, since it is larger than the sum of its proper divisors (7109891).

21329661 is an equidigital number, since it uses as much as digits as its factorization.

21329661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7109890.

The product of its digits is 3888, while the sum is 30.

The square root of 21329661 is about 4618.4045946625. The cubic root of 21329661 is about 277.3285947413.

The spelling of 21329661 in words is "twenty-one million, three hundred twenty-nine thousand, six hundred sixty-one".