661571 has 4 divisors (see below), whose sum is σ = 682944. Its totient is φ = 640200.

The previous prime is 661553. The next prime is 661603. The reversal of 661571 is 175166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 175166 = 2 ⋅87583.

It is a cyclic number.

It is not a de Polignac number, because 661571 - 2¹⁰ = 660547 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661571.

It is not an unprimeable number, because it can be changed into a prime (661541) 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 3 ways as a sum of consecutive naturals, for example, 10640 + ... + 10701.

It is an arithmetic number, because the mean of its divisors is an integer number (170736).

2⁶⁶¹⁵⁷¹ is an apocalyptic number.

661571 is a deficient number, since it is larger than the sum of its proper divisors (21373).

661571 is a wasteful number, since it uses less digits than its factorization.

661571 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21372.

The product of its digits is 1260, while the sum is 26.

The square root of 661571 is about 813.3701494400. The cubic root of 661571 is about 87.1349032297.

The spelling of 661571 in words is "six hundred sixty-one thousand, five hundred seventy-one".