661049021 has 4 divisors (see below), whose sum is σ = 661100700. Its totient is φ = 660997344.

The previous prime is 661049017. The next prime is 661049023. The reversal of 661049021 is 120940166.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 347263225 + 313785796 = 18635^2 + 17714^2 .

It is a cyclic number.

It is not a de Polignac number, because 661049021 - 2² = 661049017 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661049023) 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 3 ways as a sum of consecutive naturals, for example, 9065 + ... + 37473.

It is an arithmetic number, because the mean of its divisors is an integer number (165275175).

Almost surely, 2^661049021 is an apocalyptic number.

It is an amenable number.

661049021 is a deficient number, since it is larger than the sum of its proper divisors (51679).

661049021 is a wasteful number, since it uses less digits than its factorization.

661049021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51678.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 661049021 is about 25710.8735946486. The cubic root of 661049021 is about 871.1198074327.

Adding to 661049021 its reverse (120940166), we get a palindrome (781989187).

The spelling of 661049021 in words is "six hundred sixty-one million, forty-nine thousand, twenty-one".