1605251621 has 4 divisors (see below), whose sum is σ = 1606765644. Its totient is φ = 1603737600.

The previous prime is 1605251617. The next prime is 1605251653. The reversal of 1605251621 is 1261525061.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1261525061 = 97 ⋅13005413.

It can be written as a sum of positive squares in 2 ways, for example, as 487084900 + 1118166721 = 22070^2 + 33439^2 .

It is a cyclic number.

It is not a de Polignac number, because 1605251621 - 2² = 1605251617 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1605251321) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 755420 + ... + 757541.

It is an arithmetic number, because the mean of its divisors is an integer number (401691411).

Almost surely, 2^1605251621 is an apocalyptic number.

It is an amenable number.

1605251621 is a deficient number, since it is larger than the sum of its proper divisors (1514023).

1605251621 is a wasteful number, since it uses less digits than its factorization.

1605251621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1514022.

The product of its (nonzero) digits is 3600, while the sum is 29.

The square root of 1605251621 is about 40065.5914844646. The cubic root of 1605251621 is about 1170.8853505267.

Adding to 1605251621 its reverse (1261525061), we get a palindrome (2866776682).

The spelling of 1605251621 in words is "one billion, six hundred five million, two hundred fifty-one thousand, six hundred twenty-one".