637661 has 4 divisors (see below), whose sum is σ = 639324. Its totient is φ = 636000.

The previous prime is 637657. The next prime is 637669. The reversal of 637661 is 166736.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 481636 + 156025 = 694^2 + 395^2 .

It is a cyclic number.

It is not a de Polignac number, because 637661 - 2² = 637657 is a prime.

It is a super-2 number, since 2×637661² = 813223101842, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (637669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71 + ... + 1131.

It is an arithmetic number, because the mean of its divisors is an integer number (159831).

2⁶³⁷⁶⁶¹ is an apocalyptic number.

It is an amenable number.

637661 is a deficient number, since it is larger than the sum of its proper divisors (1663).

637661 is a wasteful number, since it uses less digits than its factorization.

637661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1662.

The product of its digits is 4536, while the sum is 29.

The square root of 637661 is about 798.5367868796. The cubic root of 637661 is about 86.0722756395.

The spelling of 637661 in words is "six hundred thirty-seven thousand, six hundred sixty-one".