6641821 has 2 divisors, whose sum is σ = 6641822. Its totient is φ = 6641820.

The previous prime is 6641813. The next prime is 6641827. The reversal of 6641821 is 1281466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 4778596 + 1863225 = 2186^2 + 1365^2 .

It is a cyclic number.

It is not a de Polignac number, because 6641821 - 2³ = 6641813 is a prime.

It is a super-2 number, since 2×6641821² = 88227572392082, which contains 22 as substring.

6641821 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 6641821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6641827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3320910 + 3320911.

It is an arithmetic number, because the mean of its divisors is an integer number (3320911).

Almost surely, 2^6641821 is an apocalyptic number.

It is an amenable number.

6641821 is a deficient number, since it is larger than the sum of its proper divisors (1).

6641821 is an equidigital number, since it uses as much as digits as its factorization.

6641821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2304, while the sum is 28.

The square root of 6641821 is about 2577.1730636494. The cubic root of 6641821 is about 187.9731080442.

It can be divided in two parts, 664 and 1821, that added together give a triangular number (2485 = T₇₀).

The spelling of 6641821 in words is "six million, six hundred forty-one thousand, eight hundred twenty-one".