661644921 has 16 divisors (see below), whose sum is σ = 1032812928. Its totient is φ = 368860800.

The previous prime is 661644877. The next prime is 661644937. The reversal of 661644921 is 129446166.

It is not a de Polignac number, because 661644921 - 2⁷ = 661644793 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661644921.

It is not an unprimeable number, because it can be changed into a prime (661644941) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 383370 + ... + 385091.

It is an arithmetic number, because the mean of its divisors is an integer number (64550808).

Almost surely, 2^661644921 is an apocalyptic number.

It is an amenable number.

661644921 is a deficient number, since it is larger than the sum of its proper divisors (371168007).

661644921 is a wasteful number, since it uses less digits than its factorization.

661644921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 768512.

The product of its digits is 62208, while the sum is 39.

The square root of 661644921 is about 25722.4594663885. The cubic root of 661644921 is about 871.3814846430.

The spelling of 661644921 in words is "six hundred sixty-one million, six hundred forty-four thousand, nine hundred twenty-one".