1981388121 has 4 divisors (see below), whose sum is σ = 2641850832. Its totient is φ = 1320925412.

The previous prime is 1981388117. The next prime is 1981388159. The reversal of 1981388121 is 1218831891.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1981388121 - 2² = 1981388117 is a prime.

It is a super-3 number, since 3×1981388121³ (a number of 29 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (1981388111) 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, 330231351 + ... + 330231356.

It is an arithmetic number, because the mean of its divisors is an integer number (660462708).

Almost surely, 2^1981388121 is an apocalyptic number.

It is an amenable number.

1981388121 is a deficient number, since it is larger than the sum of its proper divisors (660462711).

1981388121 is an equidigital number, since it uses as much as digits as its factorization.

1981388121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 660462710.

The product of its digits is 27648, while the sum is 42.

The square root of 1981388121 is about 44512.7860395190. The cubic root of 1981388121 is about 1256.0006138262. Note that the first 3 decimals are identical.

The spelling of 1981388121 in words is "one billion, nine hundred eighty-one million, three hundred eighty-eight thousand, one hundred twenty-one".