16557921 has 6 divisors (see below), whose sum is σ = 23917010. Its totient is φ = 11038608.

The previous prime is 16557917. The next prime is 16557943. The reversal of 16557921 is 12975561.

16557921 is a `hidden beast` number, since 1 + 65 + 579 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 15210000 + 1347921 = 3900^2 + 1161^2 .

It is not a de Polignac number, because 16557921 - 2² = 16557917 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (16557991) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 919876 + ... + 919893.

Almost surely, 2^16557921 is an apocalyptic number.

It is an amenable number.

16557921 is a deficient number, since it is larger than the sum of its proper divisors (7359089).

16557921 is a wasteful number, since it uses less digits than its factorization.

16557921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1839775 (or 1839772 counting only the distinct ones).

The product of its digits is 18900, while the sum is 36.

The square root of 16557921 is about 4069.1425386683. The cubic root of 16557921 is about 254.8797125870.

It can be divided in two parts, 165579 and 21, that added together give a triangular number (165600 = T₅₇₅).

The spelling of 16557921 in words is "sixteen million, five hundred fifty-seven thousand, nine hundred twenty-one".