661630221 has 16 divisors (see below), whose sum is σ = 1120220800. Its totient is φ = 378074304.

The previous prime is 661630219. The next prime is 661630231. The reversal of 661630221 is 122036166.

661630221 is a `hidden beast` number, since 6 + 6 + 1 + 630 + 2 + 21 = 666.

It is not a de Polignac number, because 661630221 - 2¹ = 661630219 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661630201) 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, 1750156 + ... + 1750533.

It is an arithmetic number, because the mean of its divisors is an integer number (70013800).

Almost surely, 2^661630221 is an apocalyptic number.

It is an amenable number.

661630221 is a deficient number, since it is larger than the sum of its proper divisors (458590579).

661630221 is a wasteful number, since it uses less digits than its factorization.

661630221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3500705 (or 3500699 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 27.

The square root of 661630221 is about 25722.1737222965. The cubic root of 661630221 is about 871.3750313313.

Adding to 661630221 its reverse (122036166), we get a palindrome (783666387).

The spelling of 661630221 in words is "six hundred sixty-one million, six hundred thirty thousand, two hundred twenty-one".