661649 has 4 divisors (see below), whose sum is σ = 671040. Its totient is φ = 652260.

The previous prime is 661621. The next prime is 661663. The reversal of 661649 is 946166.

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 661649 - 2⁸ = 661393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661679) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4589 + ... + 4730.

It is an arithmetic number, because the mean of its divisors is an integer number (167760).

2⁶⁶¹⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

661649 is a deficient number, since it is larger than the sum of its proper divisors (9391).

661649 is an equidigital number, since it uses as much as digits as its factorization.

661649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9390.

The product of its digits is 7776, while the sum is 32.

The square root of 661649 is about 813.4180966760. The cubic root of 661649 is about 87.1383275310.

The spelling of 661649 in words is "six hundred sixty-one thousand, six hundred forty-nine".