21004551 has 6 divisors (see below), whose sum is σ = 30339920. Its totient is φ = 14003028.

The previous prime is 21004549. The next prime is 21004579. The reversal of 21004551 is 15540012.

21004551 is a `hidden beast` number, since 210 + 0 + 455 + 1 = 666.

It is not a de Polignac number, because 21004551 - 2¹ = 21004549 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 (21004541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166911 + ... + 1166928.

Almost surely, 2^21004551 is an apocalyptic number.

21004551 is a deficient number, since it is larger than the sum of its proper divisors (9335369).

21004551 is a wasteful number, since it uses less digits than its factorization.

21004551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333845 (or 2333842 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21004551 is about 4583.0722228654. The cubic root of 21004551 is about 275.9123461413.

Adding to 21004551 its reverse (15540012), we get a palindrome (36544563).

The spelling of 21004551 in words is "twenty-one million, four thousand, five hundred fifty-one".