661520321 has 32 divisors (see below), whose sum is σ = 874675200. Its totient is φ = 484678080.

The previous prime is 661520297. The next prime is 661520339. The reversal of 661520321 is 123025166.

It is a cyclic number.

It is not a de Polignac number, because 661520321 - 2⁶ = 661520257 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661520351) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 201731 + ... + 204983.

It is an arithmetic number, because the mean of its divisors is an integer number (27333600).

Almost surely, 2^661520321 is an apocalyptic number.

It is an amenable number.

661520321 is a deficient number, since it is larger than the sum of its proper divisors (213154879).

661520321 is a wasteful number, since it uses less digits than its factorization.

661520321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3429.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 661520321 is about 25720.0373444519. The cubic root of 661520321 is about 871.3267821151.

Adding to 661520321 its reverse (123025166), we get a palindrome (784545487).

The spelling of 661520321 in words is "six hundred sixty-one million, five hundred twenty thousand, three hundred twenty-one".