1621801891 has 2 divisors, whose sum is σ = 1621801892. Its totient is φ = 1621801890.

The previous prime is 1621801873. The next prime is 1621801913. The reversal of 1621801891 is 1981081261.

It is a weak prime.

It is an emirp because it is prime and its reverse (1981081261) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1621801891 - 2¹³ = 1621793699 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1621801891.

It is not a weakly prime, because it can be changed into another prime (1621801801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810900945 + 810900946.

It is an arithmetic number, because the mean of its divisors is an integer number (810900946).

Almost surely, 2^1621801891 is an apocalyptic number.

1621801891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621801891 is an equidigital number, since it uses as much as digits as its factorization.

1621801891 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 37.

The square root of 1621801891 is about 40271.6015450094. The cubic root of 1621801891 is about 1174.8955732757.

The spelling of 1621801891 in words is "one billion, six hundred twenty-one million, eight hundred one thousand, eight hundred ninety-one".