621681 has 4 divisors (see below), whose sum is σ = 828912. Its totient is φ = 414452.

The previous prime is 621679. The next prime is 621697. The reversal of 621681 is 186126.

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.

It is a cyclic number.

It is not a de Polignac number, because 621681 - 2¹ = 621679 is a prime.

It is a super-2 number, since 2×621681² = 772974531522, which contains 22 as substring.

It is a D-number.

It is a plaindrome in base 14.

It is not an unprimeable number, because it can be changed into a prime (621611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 103611 + ... + 103616.

It is an arithmetic number, because the mean of its divisors is an integer number (207228).

2⁶²¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

621681 is a deficient number, since it is larger than the sum of its proper divisors (207231).

621681 is a wasteful number, since it uses less digits than its factorization.

621681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 207230.

The product of its digits is 576, while the sum is 24.

The square root of 621681 is about 788.4675009155. The cubic root of 621681 is about 85.3471843700.

The spelling of 621681 in words is "six hundred twenty-one thousand, six hundred eighty-one".