21210166681 has 8 divisors (see below), whose sum is σ = 23177788704. Its totient is φ = 19249115520.

The previous prime is 21210166673. The next prime is 21210166693. The reversal of 21210166681 is 18666101212.

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

It is a cyclic number.

It is not a de Polignac number, because 21210166681 - 2³ = 21210166673 is a prime.

It is a super-2 number, since 2×21210166681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21210166651) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1635960 + ... + 1648873.

It is an arithmetic number, because the mean of its divisors is an integer number (2897223588).

Almost surely, 2^21210166681 is an apocalyptic number.

It is an amenable number.

21210166681 is a deficient number, since it is larger than the sum of its proper divisors (1967622023).

21210166681 is a wasteful number, since it uses less digits than its factorization.

21210166681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3285431.

The product of its (nonzero) digits is 6912, while the sum is 34.

Adding to 21210166681 its reverse (18666101212), we get a palindrome (39876267893).

The spelling of 21210166681 in words is "twenty-one billion, two hundred ten million, one hundred sixty-six thousand, six hundred eighty-one".