661138 has 4 divisors (see below), whose sum is σ = 991710. Its totient is φ = 330568.

The previous prime is 661121. The next prime is 661139. The reversal of 661138 is 831166.

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

It can be written as a sum of positive squares in only one way, i.e., 660969 + 169 = 813^2 + 13^2 .

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (661139) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 165283 + ... + 165286.

2⁶⁶¹¹³⁸ is an apocalyptic number.

661138 is a deficient number, since it is larger than the sum of its proper divisors (330572).

661138 is a wasteful number, since it uses less digits than its factorization.

661138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330571.

The product of its digits is 864, while the sum is 25.

The square root of 661138 is about 813.1039293965. The cubic root of 661138 is about 87.1158890713.

The spelling of 661138 in words is "six hundred sixty-one thousand, one hundred thirty-eight".