1621838721 has 16 divisors (see below), whose sum is σ = 2278388736. Its totient is φ = 1024170576.

The previous prime is 1621838711. The next prime is 1621838761. The reversal of 1621838721 is 1278381261.

It is not a de Polignac number, because 1621838721 - 2⁷ = 1621838593 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 1621838721.

It is not an unprimeable number, because it can be changed into a prime (1621838711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 106995 + ... + 121208.

It is an arithmetic number, because the mean of its divisors is an integer number (142399296).

Almost surely, 2^1621838721 is an apocalyptic number.

It is an amenable number.

1621838721 is a deficient number, since it is larger than the sum of its proper divisors (656550015).

1621838721 is a wasteful number, since it uses less digits than its factorization.

1621838721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 228332.

The product of its digits is 32256, while the sum is 39.

The square root of 1621838721 is about 40272.0588125315. The cubic root of 1621838721 is about 1174.9044668972.

The spelling of 1621838721 in words is "one billion, six hundred twenty-one million, eight hundred thirty-eight thousand, seven hundred twenty-one".