1981509221 has 4 divisors (see below), whose sum is σ = 2085799200. Its totient is φ = 1877219244.

The previous prime is 1981509217. The next prime is 1981509253. The reversal of 1981509221 is 1229051891.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1229051891 = 32143 ⋅38237.

It is a cyclic number.

It is not a de Polignac number, because 1981509221 - 2² = 1981509217 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 (1981509721) 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, 52144961 + ... + 52144998.

It is an arithmetic number, because the mean of its divisors is an integer number (521449800).

Almost surely, 2^1981509221 is an apocalyptic number.

It is an amenable number.

1981509221 is a deficient number, since it is larger than the sum of its proper divisors (104289979).

1981509221 is a wasteful number, since it uses less digits than its factorization.

1981509221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104289978.

The product of its (nonzero) digits is 12960, while the sum is 38.

The square root of 1981509221 is about 44514.1463020465. The cubic root of 1981509221 is about 1256.0262017081.

The spelling of 1981509221 in words is "one billion, nine hundred eighty-one million, five hundred nine thousand, two hundred twenty-one".