1668521021 has 4 divisors (see below), whose sum is σ = 1669322592. Its totient is φ = 1667719452.

The previous prime is 1668520969. The next prime is 1668521027. The reversal of 1668521021 is 1201258661.

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: 1201258661 = 1117 ⋅1075433.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1668521021 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 (1668521027) 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, 397655 + ... + 401828.

It is an arithmetic number, because the mean of its divisors is an integer number (417330648).

Almost surely, 2^1668521021 is an apocalyptic number.

It is an amenable number.

1668521021 is a deficient number, since it is larger than the sum of its proper divisors (801571).

1668521021 is an equidigital number, since it uses as much as digits as its factorization.

1668521021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 801570.

The product of its (nonzero) digits is 5760, while the sum is 32.

The square root of 1668521021 is about 40847.5338423264. The cubic root of 1668521021 is about 1186.0706545537.

Adding to 1668521021 its reverse (1201258661), we get a palindrome (2869779682).

The spelling of 1668521021 in words is "one billion, six hundred sixty-eight million, five hundred twenty-one thousand, twenty-one".