661721017211 has 4 divisors (see below), whose sum is σ = 661933178400. Its totient is φ = 661508856024.

The previous prime is 661721017169. The next prime is 661721017247. The reversal of 661721017211 is 112710127166.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 661721017211 - 2¹⁴ = 661721000827 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661721017261) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106075916 + ... + 106082153.

It is an arithmetic number, because the mean of its divisors is an integer number (165483294600).

Almost surely, 2^661721017211 is an apocalyptic number.

661721017211 is a deficient number, since it is larger than the sum of its proper divisors (212161189).

661721017211 is a wasteful number, since it uses less digits than its factorization.

661721017211 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212161188.

The product of its (nonzero) digits is 7056, while the sum is 35.

The spelling of 661721017211 in words is "six hundred sixty-one billion, seven hundred twenty-one million, seventeen thousand, two hundred eleven".