661249721 has 8 divisors (see below), whose sum is σ = 736712064. Its totient is φ = 588345520.

The previous prime is 661249703. The next prime is 661249751. The reversal of 661249721 is 127942166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 661249721 - 2¹⁸ = 660987577 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661249751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 638990 + ... + 640023.

It is an arithmetic number, because the mean of its divisors is an integer number (92089008).

Almost surely, 2^661249721 is an apocalyptic number.

It is an amenable number.

661249721 is a deficient number, since it is larger than the sum of its proper divisors (75462343).

661249721 is a wasteful number, since it uses less digits than its factorization.

661249721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1279071.

The product of its digits is 36288, while the sum is 38.

The square root of 661249721 is about 25714.7763163517. The cubic root of 661249721 is about 871.2079582602.

The spelling of 661249721 in words is "six hundred sixty-one million, two hundred forty-nine thousand, seven hundred twenty-one".