1621120021 has 4 divisors (see below), whose sum is σ = 1622260672. Its totient is φ = 1619979372.

The previous prime is 1621120013. The next prime is 1621120027. The reversal of 1621120021 is 1200211261.

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 1621120021 - 2³ = 1621120013 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1621119977 and 1621120004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1621120027) 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, 568191 + ... + 571036.

It is an arithmetic number, because the mean of its divisors is an integer number (405565168).

Almost surely, 2^1621120021 is an apocalyptic number.

It is an amenable number.

1621120021 is a deficient number, since it is larger than the sum of its proper divisors (1140651).

1621120021 is a wasteful number, since it uses less digits than its factorization.

1621120021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1140650.

The product of its (nonzero) digits is 48, while the sum is 16.

The square root of 1621120021 is about 40263.1347637016. The cubic root of 1621120021 is about 1174.7308925893.

Adding to 1621120021 its reverse (1200211261), we get a palindrome (2821331282).

The spelling of 1621120021 in words is "one billion, six hundred twenty-one million, one hundred twenty thousand, twenty-one".