661378 has 4 divisors (see below), whose sum is σ = 992070. Its totient is φ = 330688.

The previous prime is 661373. The next prime is 661393. The reversal of 661378 is 873166.

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., 339889 + 321489 = 583^2 + 567^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (661373) by changing a digit.

661378 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 165343 + ... + 165346.

2⁶⁶¹³⁷⁸ is an apocalyptic number.

661378 is a deficient number, since it is larger than the sum of its proper divisors (330692).

661378 is a wasteful number, since it uses less digits than its factorization.

661378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330691.

The product of its digits is 6048, while the sum is 31.

The square root of 661378 is about 813.2514986153. The cubic root of 661378 is about 87.1264291219.

It can be divided in two parts, 66 and 1378, that added together give a square (1444 = 38²).

The spelling of 661378 in words is "six hundred sixty-one thousand, three hundred seventy-eight".