661770 has 80 divisors (see below), whose sum is σ = 1916640. Its totient is φ = 163296.

The previous prime is 661769. The next prime is 661777. The reversal of 661770 is 77166.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661777) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 15369 + ... + 15411.

It is an arithmetic number, because the mean of its divisors is an integer number (23958).

2⁶⁶¹⁷⁷⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661770, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (958320).

661770 is an abundant number, since it is smaller than the sum of its proper divisors (1254870).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661770 is a wasteful number, since it uses less digits than its factorization.

661770 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81 (or 72 counting only the distinct ones).

The product of its (nonzero) digits is 1764, while the sum is 27.

The square root of 661770 is about 813.4924707703. The cubic root of 661770 is about 87.1436390557.

It can be divided in two parts, 661 and 770, that added together give a triangular number (1431 = T₅₃).

The spelling of 661770 in words is "six hundred sixty-one thousand, seven hundred seventy".