661690 has 8 divisors (see below), whose sum is σ = 1191060. Its totient is φ = 264672.

The previous prime is 661679. The next prime is 661697. The reversal of 661690 is 96166.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 657721 + 3969 = 811^2 + 63^2 .

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

It is a super-2 number, since 2×661690² = 875667312200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661697) 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, 33075 + ... + 33094.

2⁶⁶¹⁶⁹⁰ is an apocalyptic number.

661690 is a deficient number, since it is larger than the sum of its proper divisors (529370).

661690 is a wasteful number, since it uses less digits than its factorization.

661690 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66176.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 661690 is about 813.4432985771. The cubic root of 661690 is about 87.1401273764.

The spelling of 661690 in words is "six hundred sixty-one thousand, six hundred ninety".