661624721 has 8 divisors (see below), whose sum is σ = 666785280. Its totient is φ = 656484192.

The previous prime is 661624679. The next prime is 661624729. The reversal of 661624721 is 127426166.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661624721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (661624729) 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, 65060 + ... + 74538.

It is an arithmetic number, because the mean of its divisors is an integer number (83348160).

Almost surely, 2^661624721 is an apocalyptic number.

It is an amenable number.

661624721 is a deficient number, since it is larger than the sum of its proper divisors (5160559).

661624721 is a wasteful number, since it uses less digits than its factorization.

661624721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10015.

The product of its digits is 24192, while the sum is 35.

The square root of 661624721 is about 25722.0668104256. The cubic root of 661624721 is about 871.3726168024.

The spelling of 661624721 in words is "six hundred sixty-one million, six hundred twenty-four thousand, seven hundred twenty-one".