661543 has 4 divisors (see below), whose sum is σ = 666880. Its totient is φ = 656208.

The previous prime is 661541. The next prime is 661547. The reversal of 661543 is 345166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 345166 = 2 ⋅172583.

It is a cyclic number.

It is not a de Polignac number, because 661543 - 2¹ = 661541 is a prime.

It is a Duffinian number.

It is a congruent number.

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 3 ways as a sum of consecutive naturals, for example, 2478 + ... + 2731.

It is an arithmetic number, because the mean of its divisors is an integer number (166720).

2⁶⁶¹⁵⁴³ is an apocalyptic number.

661543 is a deficient number, since it is larger than the sum of its proper divisors (5337).

661543 is a wasteful number, since it uses less digits than its factorization.

661543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5336.

The product of its digits is 2160, while the sum is 25.

The square root of 661543 is about 813.3529369222. The cubic root of 661543 is about 87.1336739277.

The spelling of 661543 in words is "six hundred sixty-one thousand, five hundred forty-three".