6621639 has 4 divisors (see below), whose sum is σ = 8828856. Its totient is φ = 4414424.

The previous prime is 6621607. The next prime is 6621649. The reversal of 6621639 is 9361266.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 6621639 - 2⁵ = 6621607 is a prime.

It is a super-2 number, since 2×6621639² = 87692206092642, which contains 22 as substring.

It is an Ulam number.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6621649) 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, 1103604 + ... + 1103609.

It is an arithmetic number, because the mean of its divisors is an integer number (2207214).

Almost surely, 2^6621639 is an apocalyptic number.

6621639 is a deficient number, since it is larger than the sum of its proper divisors (2207217).

6621639 is a wasteful number, since it uses less digits than its factorization.

6621639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2207216.

The product of its digits is 11664, while the sum is 33.

The square root of 6621639 is about 2573.2545540618. The cubic root of 6621639 is about 187.7825216432.

It can be divided in two parts, 6621 and 639, that added together give a triangular number (7260 = T₁₂₀).

The spelling of 6621639 in words is "six million, six hundred twenty-one thousand, six hundred thirty-nine".