1581201891 has 20 divisors (see below), whose sum is σ = 2416978872. Its totient is φ = 1029617568.

The previous prime is 1581201889. The next prime is 1581201899. The reversal of 1581201891 is 1981021851.

It is not a de Polignac number, because 1581201891 - 2¹ = 1581201889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1581201899) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 223506 + ... + 230471.

Almost surely, 2^1581201891 is an apocalyptic number.

1581201891 is a deficient number, since it is larger than the sum of its proper divisors (835776981).

1581201891 is an equidigital number, since it uses as much as digits as its factorization.

1581201891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 454032 (or 454023 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 36.

The square root of 1581201891 is about 39764.3293794828. The cubic root of 1581201891 is about 1165.0085384382.

The spelling of 1581201891 in words is "one billion, five hundred eighty-one million, two hundred one thousand, eight hundred ninety-one".