21172071666 has 8 divisors (see below), whose sum is σ = 42344143344. Its totient is φ = 7057357220.

The previous prime is 21172071611. The next prime is 21172071671. The reversal of 21172071666 is 66617027112.

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

21172071666 is an admirable number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1764339300 + ... + 1764339311.

It is an arithmetic number, because the mean of its divisors is an integer number (5293017918).

Almost surely, 2^21172071666 is an apocalyptic number.

21172071666 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21172071666 is a wasteful number, since it uses less digits than its factorization.

21172071666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3528678616.

The product of its (nonzero) digits is 42336, while the sum is 39.

Adding to 21172071666 its reverse (66617027112), we get a palindrome (87789098778).

The spelling of 21172071666 in words is "twenty-one billion, one hundred seventy-two million, seventy-one thousand, six hundred sixty-six".