661813 has 4 divisors (see below), whose sum is σ = 677248. Its totient is φ = 646380.

The previous prime is 661777. The next prime is 661823. The reversal of 661813 is 318166.

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 661813 - 2¹³ = 653621 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 (661823) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7653 + ... + 7738.

It is an arithmetic number, because the mean of its divisors is an integer number (169312).

2⁶⁶¹⁸¹³ is an apocalyptic number.

It is an amenable number.

661813 is a deficient number, since it is larger than the sum of its proper divisors (15435).

661813 is a wasteful number, since it uses less digits than its factorization.

661813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15434.

The product of its digits is 864, while the sum is 25.

The square root of 661813 is about 813.5188995961. The cubic root of 661813 is about 87.1455264664.

Adding to 661813 its reverse (318166), we get a palindrome (979979).

The spelling of 661813 in words is "six hundred sixty-one thousand, eight hundred thirteen".