661538443 has 4 divisors (see below), whose sum is σ = 690301008. Its totient is φ = 632775880.

The previous prime is 661538431. The next prime is 661538461. The reversal of 661538443 is 344835166.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 661538443 - 2¹⁷ = 661407371 is a prime.

It is a super-3 number, since 3×661538443³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 661538396 and 661538405.

It is not an unprimeable number, because it can be changed into a prime (661538243) 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, 14381248 + ... + 14381293.

It is an arithmetic number, because the mean of its divisors is an integer number (172575252).

Almost surely, 2^661538443 is an apocalyptic number.

661538443 is a deficient number, since it is larger than the sum of its proper divisors (28762565).

661538443 is a wasteful number, since it uses less digits than its factorization.

661538443 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28762564.

The product of its digits is 207360, while the sum is 40.

The square root of 661538443 is about 25720.3896354624. The cubic root of 661538443 is about 871.3347385549.

The spelling of 661538443 in words is "six hundred sixty-one million, five hundred thirty-eight thousand, four hundred forty-three".