1605120021 has 12 divisors (see below), whose sum is σ = 2419311648. Its totient is φ = 1023554664.

The previous prime is 1605120017. The next prime is 1605120037. The reversal of 1605120021 is 1200215061.

It is not a de Polignac number, because 1605120021 - 2² = 1605120017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 1605119976 and 1605120003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1605120001) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3876895 + ... + 3877308.

It is an arithmetic number, because the mean of its divisors is an integer number (201609304).

Almost surely, 2^1605120021 is an apocalyptic number.

It is an amenable number.

1605120021 is a deficient number, since it is larger than the sum of its proper divisors (814191627).

1605120021 is a wasteful number, since it uses less digits than its factorization.

1605120021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7754232 (or 7754229 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 1605120021 is about 40063.9491438375. The cubic root of 1605120021 is about 1170.8533529007.

Adding to 1605120021 its reverse (1200215061), we get a palindrome (2805335082).

The spelling of 1605120021 in words is "one billion, six hundred five million, one hundred twenty thousand, twenty-one".