661844821 has 4 divisors (see below), whose sum is σ = 722012544. Its totient is φ = 601677100.

The previous prime is 661844797. The next prime is 661844891. The reversal of 661844821 is 128448166.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 661844821 - 2¹³ = 661836629 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661844891) 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, 30083845 + ... + 30083866.

It is an arithmetic number, because the mean of its divisors is an integer number (180503136).

Almost surely, 2^661844821 is an apocalyptic number.

It is an amenable number.

661844821 is a deficient number, since it is larger than the sum of its proper divisors (60167723).

661844821 is a wasteful number, since it uses less digits than its factorization.

661844821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60167722.

The product of its digits is 73728, while the sum is 40.

The square root of 661844821 is about 25726.3448822409. The cubic root of 661844821 is about 871.4692314157.

The spelling of 661844821 in words is "six hundred sixty-one million, eight hundred forty-four thousand, eight hundred twenty-one".