661555 has 16 divisors (see below), whose sum is σ = 864864. Its totient is φ = 483840.

The previous prime is 661553. The next prime is 661603. The reversal of 661555 is 555166.

It is not a de Polignac number, because 661555 - 2¹ = 661553 is a prime.

It is a Duffinian number.

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 15 ways as a sum of consecutive naturals, for example, 3565 + ... + 3745.

It is an arithmetic number, because the mean of its divisors is an integer number (54054).

2⁶⁶¹⁵⁵⁵ is an apocalyptic number.

661555 is a deficient number, since it is larger than the sum of its proper divisors (203309).

661555 is a wasteful number, since it uses less digits than its factorization.

661555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 246.

The product of its digits is 4500, while the sum is 28.

The square root of 661555 is about 813.3603137601. The cubic root of 661555 is about 87.1342007757.

It can be divided in two parts, 6615 and 55, that added together give a triangular number (6670 = T₁₁₅).

The spelling of 661555 in words is "six hundred sixty-one thousand, five hundred fifty-five".