21661042664661 has 8 divisors (see below), whose sum is σ = 28881468311520. Its totient is φ = 14440656063792.

The previous prime is 21661042664551. The next prime is 21661042664699. The reversal of 21661042664661 is 16646624016612.

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

It is not a de Polignac number, because 21661042664661 - 2¹⁹ = 21661042140373 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661042664861) 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 7 ways as a sum of consecutive naturals, for example, 8441566 + ... + 10704303.

It is an arithmetic number, because the mean of its divisors is an integer number (3610183538940).

Almost surely, 2^{21661042664661} is an apocalyptic number.

It is an amenable number.

21661042664661 is a deficient number, since it is larger than the sum of its proper divisors (7220425646859).

21661042664661 is a wasteful number, since it uses less digits than its factorization.

21661042664661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19522995.

The product of its (nonzero) digits is 2985984, while the sum is 51.

The spelling of 21661042664661 in words is "twenty-one trillion, six hundred sixty-one billion, forty-two million, six hundred sixty-four thousand, six hundred sixty-one".