661491 has 12 divisors (see below), whose sum is σ = 970632. Its totient is φ = 434016.

The previous prime is 661483. The next prime is 661513. The reversal of 661491 is 194166.

It is not a de Polignac number, because 661491 - 2³ = 661483 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661421) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 55 + ... + 1151.

It is an arithmetic number, because the mean of its divisors is an integer number (80886).

2⁶⁶¹⁴⁹¹ is an apocalyptic number.

661491 is a deficient number, since it is larger than the sum of its proper divisors (309141).

661491 is a wasteful number, since it uses less digits than its factorization.

661491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1170 (or 1167 counting only the distinct ones).

The product of its digits is 1296, while the sum is 27.

The square root of 661491 is about 813.3209698514. The cubic root of 661491 is about 87.1313908462.

The spelling of 661491 in words is "six hundred sixty-one thousand, four hundred ninety-one".