16621551621 has 12 divisors (see below), whose sum is σ = 24898127072. Its totient is φ = 11081034252.

The previous prime is 16621551613. The next prime is 16621551629. The reversal of 16621551621 is 12615512661.

16621551621 is a `hidden beast` number, since 1 + 6 + 6 + 21 + 5 + 5 + 1 + 621 = 666.

It is an interprime number because it is at equal distance from previous prime (16621551613) and next prime (16621551629).

It is not a de Polignac number, because 16621551621 - 2³ = 16621551613 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 (16621551629) 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, 34200481 + ... + 34200966.

Almost surely, 2^16621551621 is an apocalyptic number.

It is an amenable number.

16621551621 is a deficient number, since it is larger than the sum of its proper divisors (8276575451).

16621551621 is an frugal number, since it uses more digits than its factorization.

16621551621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68401462 (or 68401450 counting only the distinct ones).

The product of its digits is 21600, while the sum is 36.

The spelling of 16621551621 in words is "sixteen billion, six hundred twenty-one million, five hundred fifty-one thousand, six hundred twenty-one".