16551621 has 20 divisors (see below), whose sum is σ = 24859692. Its totient is φ = 10974528.

The previous prime is 16551599. The next prime is 16551629. The reversal of 16551621 is 12615561.

It is a happy number.

16551621 is a `hidden beast` number, since 1 + 655 + 1 + 6 + 2 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 8767521 + 7784100 = 2961^2 + 2790^2 .

It is not a de Polignac number, because 16551621 - 2¹¹ = 16549573 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16551629) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 18435 + ... + 19311.

Almost surely, 2^16551621 is an apocalyptic number.

It is an amenable number.

16551621 is a deficient number, since it is larger than the sum of its proper divisors (8308071).

16551621 is an equidigital number, since it uses as much as digits as its factorization.

16551621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1122 (or 1113 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 16551621 is about 4068.3683461555. The cubic root of 16551621 is about 254.8473827254.

The spelling of 16551621 in words is "sixteen million, five hundred fifty-one thousand, six hundred twenty-one".