661557 has 8 divisors (see below), whose sum is σ = 949984. Its totient is φ = 407088.

The previous prime is 661553. The next prime is 661603. The reversal of 661557 is 755166.

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

It is not a de Polignac number, because 661557 - 2² = 661553 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 661557.

It is not an unprimeable number, because it can be changed into a prime (661553) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8443 + ... + 8520.

It is an arithmetic number, because the mean of its divisors is an integer number (118748).

2⁶⁶¹⁵⁵⁷ is an apocalyptic number.

It is an amenable number.

661557 is a deficient number, since it is larger than the sum of its proper divisors (288427).

661557 is a wasteful number, since it uses less digits than its factorization.

661557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16979.

The product of its digits is 6300, while the sum is 30.

The square root of 661557 is about 813.3615432266. The cubic root of 661557 is about 87.1342885830.

The spelling of 661557 in words is "six hundred sixty-one thousand, five hundred fifty-seven".