661943821 has 16 divisors (see below), whose sum is σ = 853741440. Its totient is φ = 498012480.

The previous prime is 661943809. The next prime is 661943827. The reversal of 661943821 is 128349166.

It is not a de Polignac number, because 661943821 - 2¹¹ = 661941773 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661943827) 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, 145986 + ... + 150451.

It is an arithmetic number, because the mean of its divisors is an integer number (53358840).

Almost surely, 2^661943821 is an apocalyptic number.

It is an amenable number.

661943821 is a deficient number, since it is larger than the sum of its proper divisors (191797619).

661943821 is a wasteful number, since it uses less digits than its factorization.

661943821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 296484.

The product of its digits is 62208, while the sum is 40.

The square root of 661943821 is about 25728.2689079541. The cubic root of 661943821 is about 871.5126812546.

The spelling of 661943821 in words is "six hundred sixty-one million, nine hundred forty-three thousand, eight hundred twenty-one".