21216055333661 has 12 divisors (see below), whose sum is σ = 22013486334972. Its totient is φ = 20446472592000.

The previous prime is 21216055333639. The next prime is 21216055333679. The reversal of 21216055333661 is 16633355061212.

It can be written as a sum of positive squares in 2 ways, for example, as 9439703208100 + 11776352125561 = 3072410^2 + 3431669^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21216055333661 is a prime.

It is a Smith number, since the sum of its digits (44) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216055303661) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 45571430 + ... + 46034631.

It is an arithmetic number, because the mean of its divisors is an integer number (1834457194581).

Almost surely, 2^{21216055333661} is an apocalyptic number.

It is an amenable number.

21216055333661 is a deficient number, since it is larger than the sum of its proper divisors (797431001311).

21216055333661 is an equidigital number, since it uses as much as digits as its factorization.

21216055333661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91606364 (or 91606333 counting only the distinct ones).

The product of its (nonzero) digits is 583200, while the sum is 44.

The spelling of 21216055333661 in words is "twenty-one trillion, two hundred sixteen billion, fifty-five million, three hundred thirty-three thousand, six hundred sixty-one".