661540 has 48 divisors (see below), whose sum is σ = 1580544. Its totient is φ = 230400.

The previous prime is 661517. The next prime is 661541. The reversal of 661540 is 45166.

It is a Harshad number since it is a multiple of its sum of digits (22).

It is not an unprimeable number, because it can be changed into a prime (661541) 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, 6772 + ... + 6868.

It is an arithmetic number, because the mean of its divisors is an integer number (32928).

2⁶⁶¹⁵⁴⁰ 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 661540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (790272).

661540 is an abundant number, since it is smaller than the sum of its proper divisors (919004).

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

661540 is a wasteful number, since it uses less digits than its factorization.

661540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 148 (or 146 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 661540 is about 813.3510927023. The cubic root of 661540 is about 87.1335422147.

The spelling of 661540 in words is "six hundred sixty-one thousand, five hundred forty".