661780 has 48 divisors (see below), whose sum is σ = 1653120. Its totient is φ = 217728.

The previous prime is 661777. The next prime is 661823. The reversal of 661780 is 87166.

661780 = T₅₁₂ + T₅₁₃ + ... + T₅₁₆.

661780 = 80² + 81² + ... + 135².

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 3979 + ... + 4141.

It is an arithmetic number, because the mean of its divisors is an integer number (34440).

2⁶⁶¹⁷⁸⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (826560).

661780 is an abundant number, since it is smaller than the sum of its proper divisors (991340).

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

661780 is a wasteful number, since it uses less digits than its factorization.

661780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208 (or 206 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 661780 is about 813.4986170855. The cubic root of 661780 is about 87.1440779957.

It can be divided in two parts, 661 and 780, that added together give a palindrome (1441).

The spelling of 661780 in words is "six hundred sixty-one thousand, seven hundred eighty".