21661043565321 has 6 divisors (see below), whose sum is σ = 31288174038810. Its totient is φ = 14440695710208.

The previous prime is 21661043565311. The next prime is 21661043565361. The reversal of 21661043565321 is 12356534016612.

It is a happy number.

21661043565321 is a `hidden beast` number, since 2 + 1 + 6 + 6 + 10 + 43 + 565 + 32 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 19478143694025 + 2182899871296 = 4413405^2 + 1477464^2 .

It is not a de Polignac number, because 21661043565321 - 2⁵ = 21661043565289 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21661043565311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1203391309176 + ... + 1203391309193.

It is an arithmetic number, because the mean of its divisors is an integer number (5214695673135).

Almost surely, 2^{21661043565321} is an apocalyptic number.

It is an amenable number.

21661043565321 is a deficient number, since it is larger than the sum of its proper divisors (9627130473489).

21661043565321 is a wasteful number, since it uses less digits than its factorization.

21661043565321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2406782618375 (or 2406782618372 counting only the distinct ones).

The product of its (nonzero) digits is 777600, while the sum is 45.

The spelling of 21661043565321 in words is "twenty-one trillion, six hundred sixty-one billion, forty-three million, five hundred sixty-five thousand, three hundred twenty-one".