1641786821 has 4 divisors (see below), whose sum is σ = 1681830444. Its totient is φ = 1601743200.

The previous prime is 1641786799. The next prime is 1641786823. The reversal of 1641786821 is 1286871461.

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 875272225 + 766514596 = 29585^2 + 27686^2 .

It is a cyclic number.

It is not a de Polignac number, because 1641786821 - 2¹⁰ = 1641785797 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 (1641786823) 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, 20021750 + ... + 20021831.

It is an arithmetic number, because the mean of its divisors is an integer number (420457611).

Almost surely, 2^1641786821 is an apocalyptic number.

It is an amenable number.

1641786821 is a deficient number, since it is larger than the sum of its proper divisors (40043623).

1641786821 is an equidigital number, since it uses as much as digits as its factorization.

1641786821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40043622.

The product of its digits is 129024, while the sum is 44.

The square root of 1641786821 is about 40518.9686566675. The cubic root of 1641786821 is about 1179.7018352755.

The spelling of 1641786821 in words is "one billion, six hundred forty-one million, seven hundred eighty-six thousand, eight hundred twenty-one".