661381 has 4 divisors (see below), whose sum is σ = 755872. Its totient is φ = 566892.

The previous prime is 661373. The next prime is 661393. The reversal of 661381 is 183166.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 183166 = 2 ⋅91583.

It is a cyclic number.

It is not a de Polignac number, because 661381 - 2³ = 661373 is a prime.

It is a super-2 number, since 2×661381² = 874849654322, which contains 22 as substring.

It is a Duffinian number.

661381 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661321) 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, 47235 + ... + 47248.

It is an arithmetic number, because the mean of its divisors is an integer number (188968).

2⁶⁶¹³⁸¹ is an apocalyptic number.

It is an amenable number.

661381 is a deficient number, since it is larger than the sum of its proper divisors (94491).

661381 is an equidigital number, since it uses as much as digits as its factorization.

661381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94490.

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

The square root of 661381 is about 813.2533430611. The cubic root of 661381 is about 87.1265608564.

The spelling of 661381 in words is "six hundred sixty-one thousand, three hundred eighty-one".