661817 has 4 divisors (see below), whose sum is σ = 712740. Its totient is φ = 610896.

The previous prime is 661777. The next prime is 661823. The reversal of 661817 is 718166.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 137641 + 524176 = 371^2 + 724^2 .

It is not a de Polignac number, because 661817 - 2¹⁴ = 645433 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661817.

It is not an unprimeable number, because it can be changed into a prime (661877) 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, 25442 + ... + 25467.

It is an arithmetic number, because the mean of its divisors is an integer number (178185).

2⁶⁶¹⁸¹⁷ is an apocalyptic number.

It is an amenable number.

661817 is a deficient number, since it is larger than the sum of its proper divisors (50923).

661817 is a wasteful number, since it uses less digits than its factorization.

661817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50922.

The product of its digits is 2016, while the sum is 29.

The square root of 661817 is about 813.5213580478. The cubic root of 661817 is about 87.1457020353.

The spelling of 661817 in words is "six hundred sixty-one thousand, eight hundred seventeen".