21666020321 has 32 divisors (see below), whose sum is σ = 26159932800. Its totient is φ = 17720640000.

The previous prime is 21666020303. The next prime is 21666020339. The reversal of 21666020321 is 12302066612.

It is an interprime number because it is at equal distance from previous prime (21666020303) and next prime (21666020339).

It is a cyclic number.

It is not a de Polignac number, because 21666020321 - 2¹⁴ = 21666003937 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21666020381) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 340421 + ... + 399021.

It is an arithmetic number, because the mean of its divisors is an integer number (817497900).

Almost surely, 2^21666020321 is an apocalyptic number.

It is an amenable number.

21666020321 is a deficient number, since it is larger than the sum of its proper divisors (4493912479).

21666020321 is a wasteful number, since it uses less digits than its factorization.

21666020321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58721.

The product of its (nonzero) digits is 5184, while the sum is 29.

Adding to 21666020321 its reverse (12302066612), we get a palindrome (33968086933).

The spelling of 21666020321 in words is "twenty-one billion, six hundred sixty-six million, twenty thousand, three hundred twenty-one".