621651661 has 4 divisors (see below), whose sum is σ = 630930112. Its totient is φ = 612373212.

The previous prime is 621651643. The next prime is 621651673. The reversal of 621651661 is 166156126.

It is a happy number.

621651661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 621651661 - 2¹⁹ = 621127373 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (621651601) 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, 4639125 + ... + 4639258.

It is an arithmetic number, because the mean of its divisors is an integer number (157732528).

Almost surely, 2^621651661 is an apocalyptic number.

It is an amenable number.

621651661 is a deficient number, since it is larger than the sum of its proper divisors (9278451).

621651661 is an equidigital number, since it uses as much as digits as its factorization.

621651661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9278450.

The product of its digits is 12960, while the sum is 34.

The square root of 621651661 is about 24932.9432879474. The cubic root of 621651661 is about 853.4584175193.

The spelling of 621651661 in words is "six hundred twenty-one million, six hundred fifty-one thousand, six hundred sixty-one".